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Chairman, Department of Biology, 
George Washington High School, New York 
Instructor in Biology, New York University 



Chairman, Department of Health, Education, 
George Washington High School, New York 

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NOV S 1929 

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Most adolescent boys and girls are more interested in themselves 
than in abstract problems. Although colleges emphasize math-, 
ematics and languages in their entrance requirements and say little 
about science, there has been a rapid growth in the number of 
sciences elected in the high schools. This is primarily due to the 
realization that science is more a part of the lives of pupils than 
other school subjects and an answer to more of their questions. 
Youth is more interested in making direct observations and reason- 
ing from them than in abstract thinking. There is a concerted 
effort to ascertain the truth about phenomena and to find out how 
and why things happen. Science teaches a valid method of inter- 
preting evidence and helps one to arrive at logical conclusions. 

In most secondary schools throughout the country elementary 
biology or general science is taught in the first or second year. 
There has been a growing demand for an advanced course in general 
biology to follow the elementary science course. This text has been 
written primarily to fill this need. The emphasis of the book is 
on problems relating to human welfare. The origin and principles 
of the development, structure, and functions of plants and lower 
animals are introduced mainly as a background for the proper 
understanding of human problems. 

An interesting and novel feature of the text is the historical 
treatment of many of the subjects, which gives the pupil a bird's- 
eye view of the entire subject without overwhelming him with 
unrelated facts. Teaching material is given at the end of each 
chapter, designed to help the pupil in organizing, in his own mind, 
the important principles discussed. The list of supplementary 
readings offers the pupil sources of information other than the 
text. All the laboratory problems necessary for a thorough 


understanding and mastery of the subject are included. These 
problems are usually given at the beginning of the chapters, so that 
the pupil may find out for himself many of the facts given later in 
the text. The pupil can exercise here the true scientific method : 
examination, observation, and confirmation of his findings. 

The plan of' presenting the subject matter is based on the prac- 
tical experience in teaching this course for several years to high 
school pupils by means of mimeographed lesson sheets prepared by 
various members of the Biology Department of the George Washing- 
ton High School, New York, N. Y. Changes in these sheets have 
been made, but much of the material has been elaborated into the 
present text. The enthusiasm of the Biology Department in the 
George Washington High School is due largely to the inspiration and 
support of Harold S. Campbell, Associate Superintendent of the 
New York high schools. In his annual report of 1928 he included 
the report of the District Superintendent of High Schools, Dr. John 
L. Tildsley. In this report, Dr. Tildsley summarized the objectives 
of science teaching and said : 

"These objectives call for the creation of a more magnificent 
self. They call for the expanding of the element of appreciation, 
the kindling of imagination, the arousing of the sense of admiration 
and wonder, the excitation of the emotions, the development of the 
power of accurate observation, the desire for truth, courage to 
follow the truth, and above all, the setting forth of science as 'a 
'way of life.'" 

The authors hope this text will open this broader "way of life" 
and inspire pupils to think and to act magnificently. 

Thanks are due the Biological Supply Co., New York, for the 
use of photomicrographs prepared by Mr. Roy M. Allen, and also 
to Miss Marjorie Fitzpatrick, Mr. Charles Inman, and Mr. Paul B. 
Mann of New York city high schools, Prof. Ralph Cheney of Long 
Island University, and Miss Ada Weckel of Oak Park, Illinois, high 
school, for their critical reading of the manuscript. 



I. The Biology of To-morrow 1 

II. The Growth of Science 10 

III. The Microscope ' 19 

IV. The History of Cells 27 

V. Functions of a Green Cell 34 

VI. Typical Animal Cell . . . * 42 

VII. The Resting and Dividing Cell 53 

VIII. Structure of Higher Plants 66 

IX. Human Tissues 73 

X. Human Tissues (Continued) 83 

XI. Food Nutrients 91 

XII. The Teeth and Their Care 107 

XIII. The Digestive System 114 

XIV. Digestion and Absorption 125 

XV. Blood and Its Importance 143 

XVI. Circulatory System 151 

XVII. Lymphatic System . . . . " . . . .163 

XVIII. The Skin and Kidneys ....... 170 

XIX. Respiration 177 

XX. Metabolism 187 

XXI. Ductless Glands 191 

XXII. The Nervous System 202 

XXIII. Nervous Reactions 215 

XXIV. Mental Hygiene 227 

XXV. How Life Began 239 

XXVI. Asexual Reproduction 246 




XXVII. Vegetative Propagation . . . . . . 255 

XXVIII. Sexual Reproduction 264 

XXIX. Reproduction of Higher Plants 273 

XXX. Reproduction of Animals 281 

XXXI. Protection of Young 292 

XXXII. Character of Offspring 306 

XXXIII. Heredity 318 

XXXIV. Mutations 335 

XXXV. Plant and Animal Breeding 343 

XXXVI. Eugenics 355 

XXXVII. Progressive Development 371 

XXXVIII. Bacteria . . . 391 

XXXIX. Beneficial Activities of Bacteria .... 403 

XL. Health 413 

XLI. Smallpox and Its Control 420 

XLII. Rabies and Its Control 429 

XLIII. Tuberculosis and Its Prevention .... 437 

XLIV. Diphtheria, Scarlet Fever, and Tetanus . . . 450 

XLV. Typhoid Fever 464 

XLVI. Certain Other Diseases 473 

XLVII. The Control of Malaria and Yellow Fever . . 480 

XLVIII. Defenses against Diseases 494 

XLIX. Immunity 504 

L. Taxonomy 510 

Appendix 529 

Index 551 



Underwood and Underwood 
Col. Charles Lindbergh. 

Underwood and Underwood 
Guglielmo Marconi. 

At no time in the history of the world have the layman and the 
scholar turned to the field of science for inspiration and help as in 
the present age. We are all becoming more scientific-minded. 
Man is leaving behind him the era of superstition and romanticism 
and is seeking the truth in the light of science. Almost daily a 
miracle happens — a discovery that thrills the world with its 
tremendous import. Newspapers and periodicals devote column 
after column to scientific matters, and even the writers of drama 
and fiction go to science for plots. People discuss present-day 
science as they once discussed literature. 

The age of science. Do you recall how interested and excited 
you were over the proposed New York to Paris flight of Charles 
Lindbergh ? The entire nation followed the preparations and the 
performance of the fearless and skillful lone pilot. All marveled 
at the tiny monoplane with its speedy Wright whirlwind motor. 
Nations rejoiced in the success of the experiment, and almost over- 
night practically all people developed an interest in aviation. They 
became air-minded. Since that time great progress has been made 
in aviation, and travel by air over certain routes has become so 
safe that few hesitate to sponsor this method of transportation. 

Not only in aviation, but in radio, color photography, and 



television, experiments have been made and are followed with 
intelligence and eagerness by great numbers of people. The radio 

Ewing Galloway 
Many of the problems of science are solved in the laboratory. 

has brought the people of our nation together again and again. 
In our own homes, by a turn of the dial, we take part in great 
public gatherings miles away, enjoy a symphony, or listen to the 
World Series baseball games. The transmission of the human voice 
and of instrumental music through miles of space is now accom- 
plished, with very little distortion. The reception of light waves, 
bringing movies into every home, is a development of to-morrow. 
There is as wide an interest in the subject matter of biology as 
in other fields. The history of many scientific experiments and 
investigations has been so wide spread that there is hardly a 
school boy or girl who does not know the story of the control 
of malaria and smallpox. The dramatic death of Hideyo Noguchi, 
of the Rockefeller Institute, occurred at the culmination of years 


of work on yellow fever. Through his experiments, he revealed 
to the entire world the painstaking methods characteristic of a 
true scientist as well as the fearless persistence of a martyr.^ 

Noguchi had solved the problem of yellow fever in South America, 
but the facts he found in that country did not seem to hold true for 
the African type of the disease. He, therefore, journeyed to' Africa 
to make further studies. He contracted the disease and died 
before completing his work. He is one of the heroes of to-day. 

What of yesterday? Consider the strides surgery has made 
since the early days of this science. For generations the chief 
medical and surgical treatments were sweating, bleeding, and 
amputations. In the Lewis and Clark expedition in 1804, one of 
the men became ill. Captain Clark described the treatment given 
him. A big hole was dug in the ground and a fire was built 
in it, in order to make the ground hot. Then the fire was re- 
moved and the man was laid on the hot earth and securely 
covered so that he would sweat. After this treatment he was 
bled. Not having any other knife, Captain Clark used his pocket 
penknife to open the blood vessel. Need- 
less to say, the man died. Among primi- 
tive people of to-day similar methods are 
still in vogue. The medicine man in a 
certain primitive tribe, still places people 
in holes heated to high temperatures, to 
sweat them. If a member of the tribe 
suffers from chronic headaches, the medi- 
cine man cuts a piece out of the sufferer's 

In Civilized Communities, Surgery, aS Physicians of yesterday practiced 

° v bleeding for many ailments. 

a scientific study, began with the hypothe- 
sis of Louis Pasteur, about 1860, that disease was usually due 
to the presence of microorganisms. Realizing that most of 
the surgical cases died from infections rather than the actual 



operation, Sir Joseph Lister (1827-1912) studied the work 
of Pasteur. Up to this time pus was always considered the 
necessary accompaniment of all wounds. Lister decided that 
germs must enter the wound from the air, from surgical instru- 
ments, or from other 
outside agencies. 
Thereafter, when oper- 
ating, he used what he 
called antiseptics to 
kill the germs. He at- 
tempted to destroy the 
germs in the air by 
spraying the air of the 
operating room with a 
carbolic acid solution. 
He then protected the 
wound as much as 
possible from contact 
with the air. All his instruments were subjected to the most 
careful antiseptic treatments. He taught his principles of anti- 
septic surgery to the surgeons of France. The Franco-German 
War broke out in 1870. It occurred to no one in France, in the 
first battles, to apply the new method of antiseptic surgery. In 
consequence, hundreds and thousands of wounded soldiers suc- 
cumbed to gangrene and septicaemia, types of blood poisoning. 
Then doctors all over the world adopted antiseptic surgery. In- 
fections which formerly followed many operations practically 
disappeared. Before Lister's time 70 per cent of all compound 
fractures resulted in death, and about 50 per cent of all major 
operations were fatal. After Lister's antiseptic methods were in- 
troduced these percentages were greatly reduced. 

What of to-day ? The most modern method of surgery is aseptic 
surgery. Germs are controlled by killing them with dry heat 

An old print shows that headache was treated by removing 
a portion of the skull. 


rather than antiseptics. It is now known that the entrance of 
germs into wounds is due to contaminated instruments or hands 
rather than to air. If the hands of the doctor and the body of 
the patient are washed with antiseptics and the instruments are 
thoroughly sterilized, there is very little chance of contamination 
from the air. The spraying of antiseptics in the air is no longer 
done. To-day, less than one per cent of the patients subjected 
to operation for compound fractures die. 

Many of the mistakes of yesterday prevail even to-day. Along 
with pure science come the pseudo-sciences. For example, 
people were taught that definite areas, of the brain controlled 
definite mental activities like motor control, vision, and judgment. 
Immediately the pseudo-science, phrenology, came into being. 
Phrenologists examined the various bumps on the head and 
claimed that these were related to the development of areas *of 
the brain. They argued that ^success in selling, teaching, or ex- 
ecutive ability could be predicted 
if the proper irregularities were 
present on the person's skull. But, 
through many years of observation 
and experimentation, it has been 
conclusively proved that the irreg- 
ularities in the skull do not neces- 
sarily follow brain irregularities. 
With the invention of the radio and 
television came a revival in the be- 
lief in telepathy and spiritualism. 

Interest in diets has led to fads 
in foods. People were told raw 
foods supplied vitamins. Some 
people began to eat nothing but raw foods such as nuts, fruits, and 
vegetables. Yeast was found beneficial in supplying a certain 
vitamin, and was at once accepted, by some, as panacea for all ills. 

Nurses who use antiseptic measures saye 
as many lives as do doctors. 


Underwood and Underwood 

What of to-morrow? The purpose of this book is to give a 
scientific biological background to pupils so that they may have 

a basis for discrimination be- 
tween real and pseudo-science 
in connection with the human 
body. The aim of all science 
is to ascertain the truth from 
unbiased experiments with- 
out regard to emotional preju- 
dices or statements based on 
speculation or imagination. 
In scientific experimentation 
one does not imagine or de- 
cide beforehand what is going 
to happen. Only actual ob- 
servable facts are accepted. 
If experiments on disease 
were prejudiced, disease 
would never be controlled. 
Similarly, all life progresses 
more efficiently when it is 
lived scientifically. The sci- 
entific, unemotional attitude 

Forestry offers an opportunity for an out-of-door toward life's problems leads 
life of service. to ft mQ ^ ex&ct so j ution> 

It is hoped that the study of biology will be an inspiration to 
recreational activities. Everyone is happy in the pursuit of a 
hobby. It gives one a worthy use of leisure time. If this hobby 
takes one out of doors, the result is usually beneficial to his health. 
If certain facts about plants and animals are understood, an in- 
telligent interest in their growth and habits is possible. News- 
papers, magazines, books, and periodicals contain many scientific 
articles and description of experiments. If a person has some 

1 M 

U. S. Forest Service 


knowledge of science, this wealth of material may be easily inter- 
preted and understood by him. The present text aims to serve 
as a basis for the interpretation of future scientific readings. 
The more interests one can cultivate the more he gets out of life. 
The relation of the biology of to-day to health cannot be over- 
emphasized. One of the reasons why the people of yesterday 
had so many fears concerning disease was that they were ignorant 
of methods for preventing and controlling it. The prevention and 
control of disease' can now be approached intelligently because 
there has been some education along these lines. Cooperation be- 
tween the public and the Board of Health is made possible because 
of this health education. The general public understands what 
the health authorities are trying to accomplish. Because it knows 
that certain restrictions are formulated in the interests of health, 
the public readily accepts and carries them out. For example, 
there is not as much opposition to' the Schick test and the sub- 
sequent immunization for diphtheria, as formerly, because the 
public has been intelligently instructed concerning the need of 
this scientific procedure to combat the disease. 

■ ^^^^^^ M HP*' «h_ 

■ i 

r U. S. Devi, of Agriculture 

Wild blueberries. Cultivated blueberries. 

Selection, cultivation and breeding have increased the size and flavor of many fruits. 

When people cultivate proper personal habits and attitudes, and 
more intelligent interests in the home and community, they achieve 




greater social and civic success. Biology helps to free people of 
ignorant and useless racial customs. It is in school that proper 
standards of cleanliness, ventilation, feeding, and routine are fre- 
quently acquired. If hygienic habits of living are developed, and 
people persist in practicing them, better social customs will soon be 
established. For example, if students are taught the importance 
of buying bread, wrapped to prevent contamination, and if they 
insist on buying only wrapped bread, the storekeepers will soon 
supply it. Weighing evidence in studying scientific data, develops 
a control which makes the student approach family problems with 
greater wisdom. Every individual owes certain responsibilities 
to his community. Problems of sewerage, garbage disposal, street 
cleaning, water and milk supply, control of disease are all discussed 
in biology classes, and a better understanding of these will give 
each person a clearer conception of his obligation to himself and 
to the public. 

The relation of biology to vocations. There are many voca- 
tional opportunities in scientific fields. Biology suggests and 
possibly lays the basis for many of these. The relation of biology 
to the study of dentistry and medicine is obvious. The achieve- 
ments of Pasteur, Koch, and Noguchi are fine ideals to arouse 
enthusiasm and interest in research work. Bacteriology, chemical 
analysis, and oral hygiene are laboratory fields that are intensely 
interesting. Nursing is a vocation with a gripping human interest. 

Science has improved the appearance, weight, and color of cattle. 


Underwood and Underwood Ewing Galloway 

Agricultural progress has been made possible largely through scientific discoveries and 


Forestry, scientific farming, and animal and plant breeding are 
vocations that constantly need more recruits. Biology has con- 
tacts with all these vocations and is a means of giving students 
such information that will help them to decide whether they 
would like to pursue a scientific vocation. 

To-morrow never comes. This book cannot give the latest 
information about living things. Before it leaves the printer's 
hands a new vitamin may be discovered, the cause and cure for 
cancer may be announced, a new and unexpected theory may 
necessitate a check and revision of much of the work that has 
been set forth in these pages. If you who read are careful in 
scrutinizing all data before you make a conclusion, you will have 
become more scientific. You may be one who will add a chapter 
to the biology of to-morrow ; you may learn and tell the farmers 
of to-morrow how to grow two blades of grass where one formerly 
grew. This Advanced Biology includes the story of the biology 
of yesterday and of to-day. If it has been well told, it should 
make your to-morrow a healthier, happier, and more complete day. 




Aristotle, Father of Biology. 

Hippocrates, Father of Medicine. 

What changes have taken place in science? What is science? 
Into what branches may science be divided? What makes up bi- 
ology ? How is biology related to other sciences ? 

Science began when primitive man made an effort to explain 
certain phenomena that he could not understand. Sickness 
occasioned much speculation. Not knowing or understanding 
anything about the various organs of the body, he thought disease 
must be due to magic. Diseases were supposed to be caused by 
evil spirits whose wrath had to be appeased or whose favor had to 
be won. Ancient people burned sacrifices or beat tom-toms to 
drive away the evil spirits. Some thought that diseases could be 
transferred from man to animals. An example of this was the 
belief that a toothache could be cured if the afflicted person stood 
on the ground under an open sky, and spat in a frog's mouth, 
asking the frog to take the toothache away. Another remedy sug- 
gested, was to keep a hot, cooked, dried bean at the right elbow 
for three days if the tooth ached in the left side of the mouth. 
The order was reversed if the tooth was on the right side. 

The advances of the Greeks. It was not until the time of Hip- 
pocrates (born about 460 B.C.) that the Greeks began to attribute 
disease to natural rather than to supernatural causes. Hippo- 
crates taught that the body was in good health when the four juices, 




blood, phlegm, yellow bile, and black bile, were mixed in the proper 
proportions. Aristotle (384-322 B.C.) was one of the first men to 
realize that all phenomena should be investigated very carefully 
before a conclusion is made. He is called the Father of Bi- 
ology because he made extensive studies of plants and animals 
and their development. Not only did he investigate, but he 
wrote down his investigations. He thus enabled the scientists 
who followed, to build on his work. Because so little dissection 
was permitted at this time, his work was full of errors ; but, 
nevertheless, his studies were 
of tremendous value. This 
was the first step in breaking 
away from idle speculation. 
He started scientific investi- 
gation, reason based on ob- 

Early surgery and medi- 
cine. Previous to the Middle 
Ages, many scientists talked 
and argued at great length 
about health and disease, but 
they were unable to make 
scientific investigations be- 
cause they were forbidden by 
law to dissect the human 
body. The only dissections 
permitted were those of lower 
animals such as dogs. Un- 
skilled barbers usually made 
these dissections for the scien- 
tists. An instructor would 

read to his class from an anatomy book written by a Greek phy- 
sician, Galen. At the same time the barber pointed out the part 

In the medical schools of the Middle Ages the 
lecturer stood in a pulpit. Barbers made the 
dissections and pointed out the structures as 
they were mentioned. A few favored animals 
received the discarded parts as they were cut off. 



of the structure mentioned in the text. It was not until the time 
of Vesalius (1514-1564) who lived in the Middle Ages, that surgery 
was put on a professional basis rather than a menial one performed 
by barbers and bath keepers. The study of the structure of the 
human body was now both permitted and encouraged. No longer 
was medical science purely speculative. It began to be based on 
observation. In lecturing, Vesalius pushed aside the clumsy 
surgeon barber and he himself demonstrated the parts of the dis- 
sected body in a proper way. He began to draw pictures of the 
dissections as he actually saw them. He disproved the old idea 
that man differed from woman by having one less rib on one side. 
He demonstrated by dissection that man and woman really have 
the same number of ribs on each side. Gradually, teaching came 
to be based on direct observation rather than opinion. As instruc- 
tors acquired more and more knowledge of the human body, they 
insisted on making their own dissections, instead of depending 
upon the unscientific efforts of barbers. They realized the value 
of careful dissections in order to show the structure of the body. 

The efforts of physicians to look 'for 
natural causes of disease rather than super- 
natural was the beginning of science, but' 
they did not go far enough. While scien- 
tists were dissecting the human body and 
disproving fallacies in regard to it, they 
were not yet checking, experimentally, ob- 
servations in the treatment of disease. For 
example, when a patient's cure seemingly 
followed the administration of some unusual 
.remedy or drug, without further experi- 
mentation, doctors jumped to the conclusion that they had dis- 
covered the cure. During anepidemic of typhus fever, a Turkish 
upholsterer, having become ill with the disease, drank some liquid 
from a pail containing pickled cabbage, and recovered. Imme- 

Before human dissections 
were made, skeletons were 
drawn very inaccurately. 




One of his drawings. 

Vesalius made many careful and accurate human dissections. He observed with exactness 
and made records with rare skill. 

diately, Turkish doctors declared cabbage juice was a cure for this 
disease. The next patient died in spite of this treatment, so they 
modified the prescription by saying that cabbage juice was a remedy 
for typhus provided the patient be an upholsterer. 

The modern scientific method. Compare these methods with 
present-day methods in science. Imagination and speculation 
have their place, but they are not to be confused with reasonable 
judgment based upon experimentation and observation. A 
scientist must have imagination and be able to predict what the 
various causes of phenomena may be. Tfeen he must test out each 
of his theories painstakingly under controlled conditions. This 
testing method must be performed repeatedly in order to allow for 
accidents. As a result of these experiments, observations are 


made and conclusions drawn. This is the modern scientific method ; 
science based on experimentation and observation. 

Consider the work of Paul Ehrlich. He wanted to find a 
chemical that had a deadly effect on certain microbes. First, he 
studied these particular disease germs by staining them different 
colors. Then he tried the effect of various chemicals on them. 
With great patience he persevered, rejecting those tests that were 
not satisfactory. Finally, his six hundred and sixth experiment 
was successful. He had found a substance which would kill the 
germ but would not injure healthy body tissue. 

Dr. Thomas H. Morgan, University of California, is now work- 
ing on the question of heredity. He has examined the size and 
various body differences of tens of thousands of tiny flies. One 
of the differences noted was a specimen with colorless instead of 
pink eyes. He has bred this and other different types through 
countless generations in his efforts to understand heredity. There 
is no wild jumping to conclusions in his work. It is based on 
definite, experimental evidence. 

Think of the late Luther Burbank. Acres of ground were tilled, 
planted, cultivated, and the plants were closely observed by this 
experimenter. All but one or two plants grown were discarded in 
his search for specimens of the plant he wanted to breed. He, 
like other scientists, examined a wealth of data and then made a 
careful selection from this material. 

Contrast the cabbage juice treatment of typhus fever mentioned 
before with the scientific investigation of malaria. It was first 
observed that people living near swamps contracted a fever ; there- 
fore, it was thought that swampy air caused this malady. The 
disease was called malaria, meaning bad air. People were cau- 
tioned to close their windows, particularly at night, to keep out the 
bad air. Then, beginning with observations based on experimenta- 
tion, doctors experimented with swampy air to see whether it would 
give malaria or not. They found that it had no direct relation to 


the disease. Then they hunted about for another probable cause. 
Due to carefully controlled experiments, doctors were able to 
demonstrate that malaria was caused by a definite microorganism 
which was carried by a certain species of mosquito. Once this had 
been demonstrated, the prevention, treatment, and cure of the 
disease followed. Certain towns along the Canal Zone, for many 
years infested with both malaria and yellow fever, have now become 
health resorts. The carrier of the germ has been exterminated and 
the disease is now under almost complete control. 

Modern experimentation solves problems under controlled con- 
ditions. The aim of the problem must be kept in mind, the method 
of procedure must be decided upon, and all conditions carefully 
regulated. All possible data must be painstakingly collected and 
arranged in an orderly manner. Judgment must be suspended 
until all the evidence has been properly weighed. All observa- 
tions should lead to a logical conclusion which will give information 
about the problem to be solved, if it does not actually solve it. 
Such scientific observation leads to straight thinking. Science is 
now becoming a philosophy of education rather than simply a 
method, and is applicable to all problems of life. 

Viewpoints of science. Human knowledge may be divided into 
the arts and the sciences. Science is careful, exact, orderly 
arranged knowledge. Among the many sciences are chemistry, 
physics, and biology. Biology is that branch of science that deals 
with living things or things that have been alive. The word 
biology comes from two Greek words, bios — life ; logos — study. 

In studying this earth on which we live, and the living things 
that are found on our globe, the different scientists may each look at 
the things about them from different points of view and use differ- 
ent units upon which to build their sciences. In physics, the 
scientist may separate a board into small chips or into sawdust, 
and divide it further into smaller and smaller particles, finally, 
reducing it to the smallest possible particle and still have the 



material, wood. When the particles become so small that they 
can be seen only with an ultramicroscope, they are called mole- 
cules. The physicist calls everything that occupies space, matter; 

and he thinks of matter as 
being made up of tiny 
molecules in motion. 

The chemist takes sub- 
stances or matter still fur- 
ther apart. Water, wood, 
rocks, air, our world in gen- 
eral, may be taken apart 
and separated into ninety- 
two 'or more different sub- 
stances called elements. 
Ninety of these have been 
separated from their com- 
pounds and studied. Most 
of the materials of the 
world, including living things, exist in the form of compounds, com- 
binations of elements. The chemist has worked out methods for 
decomposing the compounds in order to study their constituents. 
If an electric current is passed through water, it will cause the 
liquid to be separated into two gases. If these two gases are col- 
lected in tubes we find that twice as much gas will collect in one 
tube as in the other. Both gases are colorless, odorless, and taste- 
less. If a glowing splint is thrust into the tube containing the 
smaller amount of gas, it will burn brightly — the gas supports com- 
bustion. It is oxygen. If a lighted splint is held near the tube 
holding the larger volume of gas, there is a slight explosion and 
the gas burns with a blue flame. It is hydrogen. Water has been 
separated into its elements, hydrogen and oxygen, and is shown 
to consist of twice as much hydrogen as oxygen. The molecules 
of these elements may further be divided into atoms. The chemist 

Biology is related to chemistry and physics. The 
topics embraced by both biology and chemistry have 
been organized as a special science, bio-chemistry. 
Note the other combinations shown in the diagram. 




and physicist of to-day deal with matter in .even smaller particles, 
as they have discovered that atoms are further divisible into 
protons and electrons, that is, particles that carry positive^ and 
negative electrical charges. 

When a biologist looks at a living plant or animal he views it 
in the light of his particular training. To some biologists, the 
shape and form of the animal are of greatest interest. Others in- 
vestigate the processes of the living organisms. 

Biology a complex science. Many divisions of biology have 
been investigated, and there is so much known about each one 
that they are sometimes thought of as distinct subjects. The 
specialist who delves in a particular division is named in terms of 
the specialty he follows. The specialists who are interested in 
the study of bacteria (bacteriology) are known as bacteriologists. 
Protozoology, likewise, has 
protozoologists who are in- 
terested in one-celled ani- 
mals. Those who study 
snakes are interested in 
herpetology ; the specialist 
is a herpetologist. The en- 
tomologist studies insects; 
he is concerned with the 
science of entomology. 
Some scientists may special- 
ize in only one branch 
of entomology. Bugs are 
classed as Hemiptera; stu- 
dents interested in bugs are 
hemipterists. Butterflies, the Lepidoptera, are the topic of study 
of the lepidopterists. In each of these branches of biology we 
have other subdivisions — morphology, the study of the forms and 
structures, and physiology, the study of the functions of the organs. 

Biology is a complex science made of many ologies. 


Questions and Suggestions 

1. Do you know of any superstitions that persist to-day in the 
treatment of disease? Is there any scientific foundation for such 
superstitions ? 

2. What was the importance of the work of Vesalius ? 

3. Who was Aristotle ? 

4. Contrast the ancient method in treating disease with the modern 
scientific way ? 

5. In your research notebook define the divisions of biology repre- 
sented in the diagram. 

6. Give the proper names to the men who specialize in each division 

7. a. List ten or more "ologies" not given in our outline. 

b. Underline those "ologies" which might properly be included 

in the circle of biology. 

c. Place an m in front of the biological "ologies" just under- 

lined, that are morphological, a p in front of the ones that 
you think are physiological. 

Supplementary Reading 

Dana, Chas. L., Peaks of Medical History (Paul B. Hoeber [Medical Pub.]), 

chaps, i-vi. 
Locy, W. A., Biology and its Makers (Henry Holt & Co.). 
Locy, W. A., Growth of Biology (Henry Holt & Co.). 
Osborn, H. F., From the Greeks to Darwin (Charles Scribner's Sons). 



An early microscope. How some were held. 

How was the microscope invented? Was it much simpler at one 
time or is it still in its original form ? What is the use of a microscope f 
Is there a definite technique to be observed in using itf 

Biology has contacts with other sciences. Inventions and dis- 
coveries by physicists and chemists have made possible the explana- 
tions of many biological facts. It is almost impossible to discuss 
biology without including some physics and chemistry. The in- 
vention and improvement of the microscope by physicists have 
been largely responsible for the rapid progress of biology. 

The history of the microscope. In Holland, in the seven- 
teenth century, Anthony Von Leeuwenhoek (1632-1725) ex- 
perimented "with lenses, grinding hundreds and using them in 
various combinations to get different magnifications. He im- 
proved those that had formerly been used. He used dust, wood, 
and crystals to try the strength of his lenses. As he was interested 
in natural history, he investigated the minute structure of living 
things. He had little education and his researches were not con- 
ducted on an extremely scientific basis, and, therefore, his work was 
somewhat unsystematic and disconnected. However, his im- 
proved lenses opened up an entirely new field, namely, the inves- 
tigation of minute living things. Scientists could now actually 
confirm certain of their speculations. A short time before the 
microscope was improved, William Harvey, an English physician, 




had said that blood moved through the body in a circuit and that 
the beating of the heart supplied the propelling force. He had 
no microscope, but reasoned this out from observations made from 
his dissections. Leeuwenhoek ground a lens to obtain proper 
magnification, placed a tadpole in a glass tube, and adjusted the 
tube in front of the fixed lens. When he looked through the lens, 
he saw the blood, in the tail of the tadpole, come down one blood 
vessel, cross to another, and return through still another. Thus, 
by means of his lenses, he proved Harvey's reasoning was correct 
in the specimen that he was studying. Leeuwenhoek did a great 
deal to stimulate interest in perfecting the microscope. In his 
day, for each new specimen studied a new lens had to be ground 
and the object permanently fixed in relation to this magnifier. 
To-day, microscopes are constructed quite differently. The lenses 
are permanently mounted in relation to each other, forming 







Von Leeuwenhoek. 

One of his many microscopes. 
What he said: 

What he saw. 

"In the year 1675 I discover'd living creatures in Rain water which had stood but a few 
days in a new earthen pot, glazed blew within. When these living Atoms did move they put 
forth two little horns, continually moving themselves. They had a tayl, near four times the 
length of the whole body, of the thickness (by my Microscope) of a Spider web; at the end 
of which appeared a globul." 

a compound microscope. We simply change the slides on which 
the specimens are mounted. Many improvements have been made 
in microscopes since the time of Von Leeuwenhoek, and the com- 



One of Von Leeuwenhoek's microscopes con- 
sisted of a lens, embedded in a large sheet of 
copper with a movable rod which acted as a 
mount for the specimen. 

pound microscope of to-day is a very 
complicated and delicate instrument. 
It should always be handled with intel- 
ligence and care. 

Problem. Place a compound microscope 
before you and find the various parts as they 
are mentioned. 

I. There are three distinct sets of parts : 

A. The mechanical part supports the 

other parts and makes possible their controlled movements. 

B. The optical part does the actual magnifying which is made possible 
by the rays of light passing through the lenses. 

C. The illuminating part is used to direct and regulate the light. 

II. All of the mechanical parts together constitute the stand, which has a 
heavy base supporting a leg or pillar. Projecting horizontally from the top of 
the pillar, parallel with the base, is the stage. There is a hole in the middle of 
the stage through which the light passes. Above the stage is a continuation 
of the pillar, and extending from this over the stage is the arm, which carries a 
vertical tube. Projecting on both sides of the arm are disks with ridged edges. 
These are connected with a pinion that causes the tube to go up or down when it 

Von Leeuwenhoek placed a 
small aquatic animal in a glass 
tube which he fastened in 
front of a microscope. Through 
the lens he saw the circulation 
of blood in the animal's tail. 



is turned. The larger disks with the rack and pinion make up the coarse adjust- 
ment, or coarse adjustment screws. By turning the disks gently, you can see 
the effect on the tube. The coarse adjustment is used to change the distance 
between the lenses and the ^bject observed ; that is, to focus. Below the 
coarse adjustment screws is a smaller pair of disks called the fine adjustment, or 
fine adjustment screws. The fine adjustment is also used for focusing, but is 

much more delicate than the 
coarse adjustment. 

III. The optical system 
includes the part of the 
microscope containing the 
lenses. It consists of two 
sets of lenses in metal cases. 
The set placed at the lower 
end of the tube, near the 
object, is called the objective. 
On most microscopes there is 
a special attachment at the 
base of the tube for carrying 
two or more objectives con- 
veniently; this is the nose- 
piece. With the use of the 
nosepiece it is possible to change from one objective to another with no loss of 
time. The objective that is in line with the tube is the one in use. In general, 
the longer the objective, the greater is the magnifying power. Most micro- 
scopes have low-power and high-power objectives. At the top of the tube, near 
the eye, is a set of lenses in a metal case called the eyepiece. This is easily 
taken out of the tube. 

IV. The illuminating system makes possible the adjustment and focusing 
of the light on the object. It consists of the mirror, hung under the stage, and 
of the diaphragm, inserted in the opening of the stage. The mirror usually has 
two faces, one flat and one concave. The mirror can be turned in all directions 
and is used for throwing a beam of light from the window (or suitable lamp) 
upon the object and through the eyepiece, into the eye. The diaphragm 
is an arrangement for enlarging or diminishing the amount of light coming 
through the stage, by making the opening larger or smaller. 

V. Some microscopes have a joint in the pillar just below the stage, permit- 
ting the upper part of the stand to be tilted into a more convenient position. 

The microscopes of to-day vary from the kind we use in our 
school to those designed for elaborate research purposes. 



There are usually one or two clips fastened on the upper surface of the stage. 
These are slipped over the edges of the slide to hold it stationary. 

Professor R. H. Chambers has devised a microscope under which he can dissect out portions 
of a cell or inject fluids into the different parts of the cell. The drawings (upper right) show 
how he tears the cells apart. The other illustration is a photomicrograph showing a phase in 
the actual operation. 

Directions for caring for a microscope. In lifting or carrying 
the microscope, grasp it firmly by the special handle above the 
stage, and carry it in a horizontal position. Then the removable 
parts cannot fall and break. 

Allow nothing to touch any of the optical parts except espe- 
cially prepared lens paper or a clean linen handkerchief, other- 
wise the ground surfaces will be scratched. 

Before putting the microscope away, turn the nosepiece so that 
the objectives are not in a line with the tube. They are then 
protected by the stage, and the microscope is not apt to be 
damaged in placing it in the case. 

Turn the clips in so they will not be broken. 

Always follow the rules given below, for focusing. 


Rules fox* Focusing 

1. Revolve the nosepiece until the shorter objective is in a direct 
line with the tube. A click will be heard when this is'ttccomplished. 

2. Place your prepared slide on the stage so that the specimen is in 
the center of the opening of the stage. 

3. Turn the mirror toward the nearest source of light. Manipulate 
it until a bright area appears on the slide. 

4. While looking at the microscope from one side, turn the coarse 
screws clockwise until the low-power objective is one eighth of an inch 
from the slide. 

5. Then look through the eyepiece and turn the coarse adjustment 
screws toward you (counterclockwise) until the specimen is clearly 
seen. If you wish to see more of the specimen than is shown in the 
field of vision, take hold of the slide with your thumbs and slowly 
move it in different directions. 

6. Turn On your high-power objective. Listen for a click. 

7. Use your fine adjustment screws. Turn them carefully (clock- 
wise) until xne object is clearly seen. The fine screws should be used 
constantly in focusing with high power in order to see all that can be 

Problem. How does an object appear when seen through the micro- 
scope ? 

Material : Compound microscope, slide, cover slip, piece of printed paper 
with very small type. 

Method : Place a drop of water on the slide. Place a small piece of 
printed paper in the water and cover with a cover slip. The piece of paper 
is now mounted. 

Lay the prepared slide on the stage, with the object as near as possible to the 
center of the hole in the stage. Follow your rules for focusing under low power, 
then under high power. 

I. Look through the microscope at the printed letter. 

II. Describe the texture of the paper as revealed. 

III. Draw the single letter, preferably the letter " i," exactly as it appears 
under the low power. Note any apparent change in position. 

IV. By means of a ruler measure your drawing ; then measure the letter 
unmagnified. How many times does the low power appear to magnify ? 



V. Turn on the high power. Again draw the letter, or as much as you 
can see of it, as large as it appears. Measure your drawing with your ruler 
and see how many times the high power appears to magnify the letter. 

VI. Have your teacher tell you how much the microscope really enlarges 
the object with low and high power. Caution. Always find your object with 
the low-power objective, then turn on 
the high power. If you lose your high- 
power focus, go back to low power and 

Problem. How do onion cells ap- 
pear when viewed through the micro- 
scope f 

Cut an onion into halves or quarters. 
Peel off one of the scalelike leaves. 
By means of a pair of forceps or knife 
strip the thin tissue from the inside of 
the scale. Mount a part of it on a 
glass slide in a drop of water and cover 
with a cover glass. Be sure to flatten 
your specimen before covering it. View 
the material under the microscope. 
Then remove cover glass, and stain 
the material by adding a small drop of 
dilute iodine solution. Again cover. Ob- 
serve with low power, then high power. 

I. The little divisions that make up 
the onion membrane are called cells. 

A. The boundary of each cell is 
the cell wall. 

B. Describe the color and shape 
of these cells. 

The cells of the onion tissue often show 
the heavy, woody walls and the large vacuoles 
that are characteristic of most plant cells. 

II. Observe the position of the granular and clear areas. The granular 
areas make up the living part of the cell and are composed of a material called 
cytoplasm. The clear areas are the vacuoles or fluid-filled spaces in the cytoplasm. 

III. Find a small dense area somewhere in the cytoplasm. This is the nucleus. 
A. Each nucleus has two disklike structures called nucleoli. Try to 

identify a nucleolus in a nucleus. 

WH. FITZ. AD. BIO. — 3 

/ O f 


IV. Make the following drawings in your research notebook : 

A. A careful diagram of a group of cells five times as large as they 
appear under low power. 

B. A group of cells twice as large as they appear under high 
power. Label cell wall, cytoplasm, vacuole, nucleus, nucleolus. Under 
the drawing, in small figures, state how many times enlarged your draw- 
ing has been made ; for example, X 4 ; X 5 ; X 2. 


1. What is the difference between a simple and a compound micro- 
scope ? 

2. Classify the parts of a microscope into three divisions. 

3. Name two effects a microscope has on objects. 

4. Explain how to focus with the low power ; with high power. 

5. Why can we focus only thin material with our compound 
microscopes ? 

6. How do you mount a specimen, for study under the compound 
microscope ? 

Supplementary Reading 

Locy, W. A., Biology and Its Makers (Henry Holt & Co.). 

Locy, W. A., The Growth of Biology (Henry Holt & Co.). 

Traeger, Alfred, The Microscope (E. Leitz Inc., 60 East 10th St., N. Y.). 

Robert Hooke's microscope. 



What he said: 

What he saw and drew. 

" I took a good clear piece of Cork, and with a Pen-knife sharpened as keen as a Razor, J 
cut a piece of it off, and thereby left the surface of it exceedingly smooth, then examining it 
very diligently with a Microscope, me thought I could perceive it to appear a little porous, 
much like a Honey-comb." 

How were living things first investigated? What were some of the 
results of these studies? What scientists contributed to this work? 

The pages of history reveal how and by whom the terms used in 
describing the cell have been given to the science of biology. It 
was comparatively easy for us to find the structure of an onion cell 
under the compound microscope, but it has taken scientists three 
centuries to perfect the microscope and find out as much about 
cells as is known to-day. 

The cell as first described. With very crude lenses, arranged 
something like those in our compound microscope, Robert Hooke 
(1635-1703), an Englishman, examined a thin section of cork. He 
saw little boxlike structures which he called cells. He drew 
diagrams and published the results of his investigations. He saw 
only the cell wall after the living matter had disappeared, but the 
term cell, first used by him, has been retained. 

The nucleus. Robert Brown (1773-1858) was a Scotchman. 
He studied medicine and became a surgeon's mate of a British 
regiment in Ireland. During his early years, and while connected 
with the army, he collected and studied plants and became known 
as a naturalist. In studying orchids, he discovered a structure in 



the cells which he called the nucleus ; and later he found a like 
structure in the cells of many other plants. He wrote the following 
account of his discovery: "In each cell of a great part of the 
orchid family, a single circular area, generally somewhat more 
opaque than the membrane of the cell, is observable. The 
nucleus of the cell is equally manifest in many other fam- 
ilies. ..." 

Theodore Schwann (1810-1882) found, as a result of careful 
work, that all the animals he investigated were made of cells. 
At »the same time a friend of. his, Matthias Schleiden, discovered 
that all of the plants he observed were made of cells. In the 
cells they studied, they both noted the nucleus that Brown had 
first discovered. They then made the supposition that all living 
things are made of cells. This became known as the cell theory, 
and this theory, having since been checked and rechecked by 
many scientists, and more facts added, is now accepted as a fact. 

Protoplasm was discovered by a French naturalist, Felix Dujar- 
din, in 1835, and named by Purkinje in 1840. But the scientist 
who made the name protoplasm best known was Hugo von Mohl 
(1805-1872). He was born in Stuttgart, Germany. He was 
graduated in medicine from Munich, became a professor of phys- 
iology at Berne, and later a professor of botany at Tubingen. He 
observed and analyzed the cell contents and described the move- 
ment in the cell of certain small bodies which later were termed 
chloroplasts. These were later shown to be the structures that 
contain green coloring matter. He brought into general use the 
term protoplasm and the fact that it is a living, streaming, grow- 
ing, dividing substance. 

Problem. How do the cells of Elodca appear when viewed through the 
microscope f 

Examine the appearance of a single leaf of the Elodea. Mount it in 
water and heat by holding in the palm of the hand for a few minutes. The 
heating will activate the protoplasm. Focus with low, then high power. 


By slowly changing the focus you will be able to see that the Elodea leaf 
is made of more than one layer of cells. 

I. What striking difference do you observe between Elodea and onion 
cells ? 

II. Describe the new structures that you observe in Elodea cells. These 
are called chloroplasts or green color bearers. 

III. Observe two conspicuous differences between the chloroplasts and the 
rest of the cytoplasm. 

IV. Trace the movement of the chloroplasts. Do they move around in 
the individual cells or do they pass from cell to cell? Suggest a reason for 
your answ r er. The chloroplasts are carried by the movement of the stream- 
ing protoplasm. 

V. Remove the cover glass, add a drop of dilute iodine, re-cover, and 
mount again. 

VI. Describe the structures you now observe, that were also present in the 
onion cell. 

VII. Make a diagram, times five, of a few of the cells of the Elodea. By 
means of arrows, trace the pathway of the moving chloroplasts. Label cell 
wall, cytoplasm, nucleus, vacuole, chloroplast. 

Protoplasm, an active substance. The movement of protoplasm, 
observed by you in Elodea, was first observed by Von Mohl. He 
recognized that the living, streaming, moving protoplasm was / the 
cause of the motion that we observed in our Elodea cells. 

Another name should be* added to the list of those who devoted 
a large amount of their time to the study of the cell. Max 
Schultze, a German anatomist, in 1863, clearly brought out the 
fact that protoplasm (nucleoplasm and cytoplasm) is the unit of 
all physiological activities. Before his time, people thought that 
plant cells were made of one kind of living material and animal 
cells of another kind. Much has been added to the work of 
Schultze, but many of the facts discussed in the following para- 
graph are largely a result of his efforts. 

The key to every biological problem is sought in the cell ; for 
every living organism is, or at some time has been, a cell. As 







a result of the studies of 
the scientists previously 
named, the cell theory was 
further developed. It was 
now stated that all plants 
and animals are made of 
cells and cell products. 
The cell is the structural 
and physiological unit of 
the organism. The living 
organism can perform cer- 
tain functions because its 
cells are adapted to per- 
form these functions. 
Other scientists, using this 
theory as their basis, have 
been able to show the im- 

Compare the cells of Elodea shown in the diagram with portance of the Cell in the 
those you studied under the microscope. •, ■> n • 

development or organisms 
and something of its importance in heredity. Many scientists 
are still investigating the structure and functions of cells and 
others are studying the cell in its relation to the development of 
the organism. This work, in spite of the fact that three centuries 
have passed, is still in a developmental stage. 

Cellular nature of plants. The cells of green plants are not all 
alike in size and shape. A narcissus leaf is made of many layers 
of cells which vary in shape. 

Problem. Study of the epidermis of the narcissus leaf. 

I. Peel off a small strip of the thin lower surface (epidermis) of a narcissus 
leaf. Mount it for study, and focus it under the microscope. 

A . Describe two different kinds of cells that are seen. 

B. Note the small oval opening between paired cells. Suggest a use 
for these openings ; for the cells that form them. 



II. Draw a few of the cells, making sure to include in your diagram, at 
least two differently shaped ones. 

Higher plants are composed of many cells, but certain plants 
are very simple in structure. A green coating is frequently found 
on the north side of many buildings and of most trees. This is 
caused by the presence of thousands of tiny one-celled, green 
plants called Pleurococcus. 

Problem. Study of Pleurococcus. 

I. Scrape some of the green material on to a slide, mount in water, and 
study with low and high magnification. Describe the shape, color, and struc- 
ture of the cells. 

II. Draw a single cell and a group of cells. Label cell wall, the very large 
chloroplast which almost fills the cell, and the nucleus. 

III. Write a description of what you have seen and tell how Pleurococcus 
differs from Elodea and narcissus cells. 

A typical green cell that is easy to study is Spirogyra. As it 
floats on the surface of ponds, it looks like a tangled mat of 
green threads or hairs. A 
common name for it is pond 
scum or frog's "spittle." 
This latter name is given to 
it because it is slimy in tex- 
ture and is found in the same 
habitat with frogs. Many 
people at one time thought 
that the frogs spit it out. 

Problem. Study of the cells 
of Spirogyra. 

By means of forceps and a pair 
of scissors detach a few strands of 

Spirogyra. Mount them on a slide and cover with a cover slip, 
the specimen under the low power. 

A photomicrograph of the lower surface of a leaf. 




I. Describe the cellular structure of a single strand of Spirogyra. When- 
ever unicellular plants exist singly, end to end, the formation is called a filament. 

In reality, each cell is a complete unit and 
in no way dependent on the adjoining cells. 

II. Describe a structure in the cell that 
suggests the reason for the name Spirogyra. 
The name Spirogyra means coiling circles 
(spira — coil; gyros — circle). What re- 
semblance is there between a chloroplast of 
Spirogyra and a chloroplast observed in the 
Elodea ? 

III. State the number of complete chlo- 
roplasts observed in each cell of your 

A. State the number of complete 
turns found in each chloroplast. 

B. Using the words waVy, irregular, 
or straight, describe the edge of the 

IV. Identify the cell wall and the fila- 
ment sheaths. This sheath is gelatinous 
and gives the strands their characteristic 
slimy texture. 

V. Draw a 'cell five times larger, than 
the one observed under the low power. 
Show in your drawing how the adjoining 
cells lie in relation to the one drawn. Label 
cell wall, filament sheath, chloroplast. 

VI. Stain a cell with dilute iodine and focus under low power and then 
under high power. Locate and describe the nucleus, nucleolus, and strands 
of cytoplasm. 

VII. Describe the location and suggest the nature of the contents of the 
vacuoles left among the strands of cytoplasm. The part of the cytoplasm 
inclosing the vacuoles is called the plasma membrane. 

VIII. Locate the structures stained blue. These are specialized cyto- 
plasmic structures called pyrenoids. What evidence is present that the pyre- 
noids store starch? 


- nucleus* 


..vccCLcqle. ^ 

cell sap & 

— filaments 

S'pirogyra is a single-celled plant. 
These plants grow end to end and 
thus form strands called filaments. 


IX. Draw a complete cell of Spirogyra as observed under the high-power 
objective. Label filament sheath, cell wall, strands of cytoplasm, plasma 
membrane, vacuole, nucleus, nucleolus, spiral chloroplast, and pyrenoid. 

X. Write a description of Spirogyra, mentioning all the parts that you saw. 

The simplest plants have no root, stem, 
nor leaves. Such plants are called Thal- 
lophyta {thallus — shoot ; phyton — plant) . 
The green thallophytes are called algae. 
Their color is due to the presence of chloro- 
plasts that vary in size and shape. The 
algae that we have already studied are 
Pleurococcus and Spirogyra. Other thai- ^ wm ^^^^ a ^ 9 
lophytes lack chloroplasts and are usually 

colorless. They are called fungi. Yeasts and molds are common 
examples of fungi. 


1. Outline in tabular form, the names of the scientists, their nation- 
alities, century in which they worked, and their contributions to the 
cell theory. 

2. Draw as many labeled cells as are necessary to show cell wall, 
nucleus, cytoplasm, vacuole, pyrenoid, and chloroplast. 

3. Compare Spirogyra with another alga that you have studied. 

4. What makes Spirogyra slimy ? 

5. What is a reason for the name thallophytes ? 

Supplementary Reading 

Gager, C. S., General Botany (P. Blakiston's Son & Co.), chap. ii. 

Haupt, A. W., Fundamentals of Biology, (McGraw-Hill Book Co. Inc.), 

chap. iv. 
Holman, L. A., and Robins, W. W., Textbook of General Botany (John Wiley & 

Holmes, S. J., General Biology (Harcourt, Brace & Co.), chap. iii. 



Nature's food factory. 

Some of the products. 

What does a green cell use for foodf Where does it get this food? 
What are the physiological activities of cells containing chlorophyll f 

In order to live, a green cell must carry on certain functions. Be- 
cause these functions are carried on within the organism they are 
called physiological functions. These functions may be classified 
as nutritive^ adaptive, and reproductive. The nutritive processes 
can be further subdivided into absorption, food manufacture, food 
storage, digestion, assimilation, secretion, growth, respiration, and 
excretion. These have to do with the obtaining and the using or* 
food. The adaptive processes have to do with the way the organism 
maintains itself and behaves in its environment. The reproduc- 
tive processes have to do with the producing of new individuals. 

Absorption. The Spirogyra takes in carbon dioxide, water, and 
mineral matter for the manufacture of food. These raw materials 
are in the form of gases and solutions and enter through the cell 
membrane. They remain in the vacuoles until they are needed. 
Oxygen, also, is taken in during the breathing process. The 
process by which material passes through a cell membrane is called 
osmosis or absorption. Many theories are advanced to explain 
this activity ■; but probably no-one theory holds under all condi- 
tions. According to one explanation there are minute openings in 
the membrane through which the liquid or gas passes. 



According to the molecular theory, all matter, whether solid, 
liquid, or gas, consists of molecules in constant motion. The mole- 
cules of solids are close together and there is very little space for 
them to move. There is more space between the molecules of 
liquids, and still more between those of gases. Consequently, 
molecules of liquids move more freely than those of solids, and 
molecules of gases move even more freely than those of liquids. 

As the molecules in gases or solutions keep bounding up 
and down, knocking against each other and against the cell mem- 
brane, some of them move through the small openings. If the 
molecules are very active, as in gases or certain liquids, these 
molecules can pass readily through the membrane. The mole- 
cules of denser liquids move more slowly and therefore will take a 
longer time to go through the membrane. In general, the rate of 
osmosis of a substance depends upon the number of its molecules. 
During the process of osmosis the molecules of any substance 
pass through a permeable membrane more rapidly from the area 
of greater concentration to an area of lesser concentration. Osmosis 
never stops, although when there is a balance of materials on 
either side of the membrane, there may be so even an exchange 
of molecules that osmosis is not obvious. When the membrane 
is a living one, as in the cell membrane, the cytoplasm exercises 
a definite selective action, taking in and keeping in the materials 
needed by the cell and eliminating those not needed. 

Demonstration. To illustrate the movement of molecules. 

Make a very dilute solution of powdered carmine or India ink in water. 
Place a drop under the compound microscope and observe under both low and 
high magnification. 

Describe the behavior of the particles observed in this experiment. 
According to the molecular theory, molecules are always in a state of motion 
somewhat similar to that of the particles observed by you. 

Robert Brown, who was the first person to observe the nucleus 
in plant cells, first described the movement that you have just 


observed. This is called the Brownian motion. Modern physics 
teaches that molecules move not only in solution and during 
osmosis, but that the molecules of all matter are constantly bom- 
barding each other. The desk on which you write is composed 
of tiny particles not inseparably cohering and sticking to each 
other, but in a slight, constant state of activity similar to that 
which you observed in the particles under the microscope. 

Food manufacture. A green cell is one containing certain organ- 
ized and specialized cytoplasm, called chloroplasts. There is 
found in these chloroplasts a complex, green material, chlorophyll, 
which is necessary for the manufacture of food. The green cell is 
independent because it does not rely on other organisms for its 
food ; it manufactures its own. All cells, whether green or not, need 
carbohydrates (sugar and starches), fat, and protein. The cells 
manufacturing foods always absorb two compounds : a gas, carbon 
dioxide (C0 2 ), and water (H 2 0). These raw materials get through 

O -for Ojci&<jdforL- 

co 2 

■ «£ energy 

'^nitrates. * 

There is a continuous income and outgo of gases during respiration and photosynthesis. 

the cell wall and plasma membrane by the process of osmosis. 
Then the chloroplasts by a number of complicated processes, with 
the aid of sunlight, chemically tear apart the elements of these 
compounds, water and carbon dioxide, and recombine them into 
simple carbohydrates. Since more oxygen is contained in the raw 
materials than in the sugar manufactured, oxygen is given off 
during the process. It is supposed by some that the elements 



carbon and oxygen, found in the compound carbon dioxide, chemi- 
cally join with the elements hydrogen and oxygen, found in the 
compound water, and give rise to a more complex compound of 
carbon, hydrogen, and oxygen, probably formaldehyde. In this 
chemical process, oxygen is left over and is given off by the plant. 

C0 2 + H 2 

Carbon dioxide + Water 

■>- CH 2 + 2 

->- Formaldehyde + Oxygen 

This process is one of the early 
light ; syn ^— together ; tithemi - 
Photosynthesis is the combining 
chlorophyll, in the presence of 
light, to make sugar. 

The molecule of formalde- 
hyde is then chemically joined 
with other molecules of formal- 
dehyde to make a simple sugar. 
Further combining will build up 
more and more complex sugars 
such as monosaccharides, di- 
saccharides, polysaccharides 
(starch is in this group) . Some- 
times other complex compounds 
such as oils and fats are pro- 
duced. These are often found 
in cells as storage products. 
They are again converted into 
simpler forms of sugar when 
they are to be used as fuel. 

Sugar is also the basis for 
the formation of proteins. In 
order to manufacture protein — 
a process known as protein- 

steps in photosynthesis (phoso — 
-place: light places together), 
of carbon dioxide and water by 


needle like 


Cells may contain inclusions such as plastids 
(color-bearing particles), starch granules or 
crystals of various forms. 


synthesis — the plant absorbs minerals, in the form of nitrates, 
sulphates, and phosphates, which are dissolved in soil water. These 
substances furnish the plants with nitrogen, sulphur, and phos- 
phorus which are thought to combine with some of the sugar to 
form protein, a substance containing carbon, hydrogen, oxygen, 
nitrogen, sulphur, phosphorus, and perhaps other minerals. 
Protein in protoplasm may be represented by the symbols 
C-H-O-N-S-P. Most protein is used for growth (protoplasm 
making), repair, and storage. Some is decomposed and the sugar 
(one of the products of decomposition) is burned as fuel, while 
the other products are thrown out as nitrogenous wastes or stored 
for further protein-synthesis. 

Digestion. When the food substances that have been stored 
in the cells of the plant as fats, starches, and proteins are to be used, 
they must first be changed to a soluble form. The process of 
changing an insoluble nutrient into a soluble form that can be 
used by the organism is called digestion. Digestion is brought 
about by the presence and action of chemical substances called 
digestive enzymes. These act as catalytic agents, that is, they 
bring about a chemical change, but are themselves not affected 
by nor changed during the process. In the cell where digestion 
takes place, there is an amylase for the breaking down of starch, 
a protease for the digestion of proteins, a lipase for the digestion 
of fats. (The names of most of the enzymes end in ase.) After 
being digested, the liquid nutrients may be carried by means of 
the streaming, flowing motion of the protoplasm to that part of 
the cell where they are to be utilized. If there is an excess of 
food nutrients, they may again be combined into an insoluble 
form and stored in the cells until needed. 

Respiration. Each living plant cell takes in oxygen through the 
cell membrane and gives off carbon dioxide by means of diffusion. 
The oxygen unites with the compounds of hydrogen, oxygen, and 
carbon and releases the energy, in the form of heat, stored in them. 


This union is a type of oxidation. The energy released from 
food was stored up at the time of the manufacture of food (photo- 
synthesis and protein-formation) in a potential, latent or dormant 
form. The sun is the source of this energy. When oxidation of 
food occurs, the potential energy is converted and released as 
kinetic, an active form of energy. In plant cells, the kinetic 
energy takes the form of work energy or heat energy, resulting 
in the maintenance of a normal temperature. As a part of this 
oxidation process, wastes, carbon dioxide and water, are formed. 

carbohydrate "bg^tjy cc ^rot^ii^ 

[CHpc(p( ICHadj^SP" 

2 O* 

\ releccsecl Y 

er ^" ~ ~ u r\~Z nitrogenous 

The green plant cell builds up carbohy- A protein may be broken down during oxi- 

drates which contain bound-up energy. This dation and energy released. Among the 
may later be set free as heat or work energy. resulting wastes are some containing nitrogen. 

These the cell gives off. If respiration takes place at the time 
the plant is actively making sugar, the carbon dioxide and some 
of the water resulting from oxidation may be retained for further 
photosynthesis. Nitrogenous wastes are probably retained for 
further manufacture of protein. The oxygen released during 
photosynthesis may be retained for oxidation although it is usually 
given off. Thus a balance of materials may be maintained. Res- 
piration, then, involves the taking in of oxygen, the oxidizing of 
. certain food materials present, and releasing energy and waste 
products. The respiration process is the means of releasing all of 
the energy needed by the plant. 

Assimilation. The protoplasm of the cell is built of the elements 
C-H-O-S-N-P, and sometimes others. After protein manufac- 
ture is accomplished, the lifeless protein together with water and 



mineral materials may ultimately be transformed into living plant 
protoplasm. Scientists have not determined just how this trans- 

n i -* 

© + joocU- 

, "more 


A green cell makes and assimilates food. Growth occurs. When no further growth is pos- 
sible, the nucleus elongates, divides, and then the cell divides. Thus two cells are formed. 

formation takes place. The name given to the change of a soluble 
protein into living protoplasm is called assimilation. True growth 
in an individual cell is due to the increase in the sum total of the 
amount of protoplasm resulting from assimilation. Cells may also 
increase in size, temporarily, when the cell vacuoles become filled 
with an abundance of watery sap. The entire plant organism 
grows by enlargement of the individual cells, until they attain a 
certain size. Then they divide, causing an increase in the total 
number of cells. This process of cell division will be discussed later. 

Excretion. Any product given off through the cell wall as waste 
is called an excretion. If a product is built up and given off for a 
further use in the organism, it is called a secretion. Often, some 
oxygen formed during food manufacture is held and used for oxi- 
dation. The waste products from oxidation of sugars are carbon 
dioxide and water. When these wastes are not retained by the 
cell for further food making, they are excreted through the cell wall. 

Irritability. There are many substances and forces, called 
stimuli, that act upon a green plant cell. A cell is spoken of as 
being sensitive or irritable to light, temperature, touch, chemicals, 
electricity, and many other stimuli. The real cause of the effects 
produced by these stimuli is to be found in the nature of pro- 
toplasm. It is the protoplasm" that is irritable. Response is the 
name given to the reaction the organism makes to the stimulus. 
We have seen the effect on the protoplasm of the Elodea cell by 


holding it in a warm hand for a few seconds. Other stimuli have 
other effects depending upon the sensitiveness of the particular cell. 
Cell division. A plant cell has a certain limit of size beyond 
which it does not grow. When this limit is reached, the nucleus 
may elongate and divide, producing two nuclei. There is a wall 
formed across the cell dividing the protoplasm into two parts, 
each containing one of the daughter nuclei. 


1. Why may chlorophyll be considered the source of the food supply 
of the world ? 

2. Discuss the transformations of energy in a green plant. 

3. If green plants are eaten by animals, what additional trans- 
formations of energy may result ? ' 

4. Compare the oxidation of food in the plant cell with the oxidation 
of coal in the school furnace, giving points of similarity and difference. 

5. Compare respiration in a green plant cell with photosynthesis, 
considering materials used, products formed, products excreted, and 
the purpose of the functions. 

6. Why may carbon be considered the real fuel of a green cell ? In 
what form did it enter the cell? In what form did it ultimately 
leave the cell ? Name all physiological functions involved in the use 
of carbon. 

7. Trace the probable source of the carbon in coal. 

8. Discuss a balanced aquarium, stating the give and take of 
materials between fish and green plants. 

9. In the figure on page 36 the possible intake and outgo of 
materials in a green cell are shown. What are the actual interchanges 
of materials ? 

Supplementary Reading 

Coulter, Barnes, and Cowles, A Textbook of Botany (American Book Co.), 

Vol. I. 
Gager, C. S., General Botany (P. Blakiston's Son & Co.). 
Holmes, S. J., General Biology (Harcourt, Brace & Co.), chap. vii. 




and of Paramecium. 

Photomicrographs of Amoeba 

Bo animals ever consist of single cells f Can the simplest of animals 
be easily recognized as animals f Bo they appear different from one- 
celled plants? Bo they perform the same physiological activities f 

Laboratory exercise. Study of an amoeba (amoibos — changing). The 
amoebas belong to the branch of animals called Protozoa (protos — first ; zoon — 
animal : first or early animal). To locate amoebas, scrape the undersurface of 
the leaves of Elodea on to a glass slide. Add a drop of water and cover with a 
cover glass. Another method for finding amoebas is to crush some pond lilies 
or other water plants and let the mass remain undisturbed for a few weeks. 
Tiny animals will usually be found in the scum which forms. Mount some of 
the scum and locate an amoeba with low power, then study it with high 
power. Later stain with iodine and again observe. 

I. Describe the amoeba, including shape, color, and number of cells. 

II. How does its shape differ from any cell previously observed? The 
irregular projections of protoplasm are called pseudopodia or pseudopods 
(pseudo — false; podium — foot). What seems to be the function of the 
pseudopodia or false feet ? 

III. Describe the movement of the animal. Suggest a reason for the 
name amoeba. 

IV. After staining it with iodine, find cytoplasm, nucleus, * and a space 
called the contractile vacuole. The clear outer protoplasm of the cell is called 
ectoplasm and the granular inner area is endoplasm. 

V. State three structures found in the Spirogyra not found in the amoeba, 
and one structure found in the amoeba not found in the Spirogyra. 

VI. State a difference in nutrition between Spirogyra and amoeba. 




VII. Name a function performed by the amoeba that the green cell cannot 
perform. What is the value of this function to an animal organism ? 

VIII. Make a drawing three inches in diameter, of an amoeba, and label 
cytoplasm, nucleus, plasma membrane, pseudopodia, and vacuole. 

Life functions of an amoeba. Ingestion. When an amoeba 
comes in contact with a particle of food, it throws out pseudopo- 
dia which flow over and around the food. The food particle is then 
taken into the cytoplasm. This engulfing of food by the amoeba 
is its method of food getting, or ingestion. The amoeba shows little 
power of selection of food. It takes in almost anything small enough 
to be engulfed. The cytoplasm encloses the food and forms a vac- 
uole or bubble encircled by plasma membrane. The food and 
some fluid deposited by the cytoplasm are inside the vacuole. 

Digestion. The engulfed food is principally smaller microor- 
ganisms and particles of plants. These consist of combinations of 
the nutrients, proteins, fats, and carbohydrates. The particles cir- 
culate in the streaming cytoplasm in the form of a food vacuole. 
The cytoplasm secretes aw 

5 ^. r ^4n3k>pWm/ 



>< : vacuole 

digestive enzymes to con- 
vert these nutrients into a 
soluble form which can 
then be assimilated by the 
protoplasm. As the circu- 
lating protoplasm carries 
the food around the cell, 
the digestive enzymes, pro- 
tease, lipase, and amylase, 
gradually dissolve the nu- 
trients in the food. These 
nutrients pass through the 
plasma membrane of the vacuole by osmosis and mingle with 
the cytoplasm. The indigestible materials that have entered with 
the food may be eliminated from any part of the organism. 

Amoeba may assume a variety of shapes. Compare 
the animals you studied under the microscope with 
these diagrams. 



Assimilation. The digested protein together with water and 
absorbed mineral matter are converted into protoplasm by the ac- 
tivity of the cytoplasm of the 
living amoeba. This is as- 
similation. As a result of as- 
similation, new protoplasm is 
formed and the animal grows. 
Respiration. Oxygen from 
the air in the water may 
enter through any part of the 
surface of the amoeba. It 
meets the digested nutrients 
in the cytoplasm and oxida- 
tion takes place, that is, oxy- 
gen combines with carbon and 
hydrogen compounds. As a 
result of oxidation, energy is 
released. This energy en- 
ables the amoeba to carry on 
its functions. Since protein, fat, and sugar contain carbon and 
hydrogen, carbon dioxide and water are oxidation products. 
Protein gives rise to nitrogen, sulphur, and phosphorus products, 
also, one of which, urea, is a nitrogenous waste. The wastes 
resulting from oxidation are collected in the contractile vacuole. 
This bursts and expels the wastes through the plasma membrane 
into the surrounding water. 

Reproduction. When the amoeba reaches a certain maximum 
size natural to its species, the nucleus divides in two parts and 
then the entire cell cleaves in two equal parts. This results in the 
production of two distinct cells each with its own nucleus. This 
process is called reproduction by fission. 

Irritability. The amoeba is very sensitive to outside stimuli. 
If it is touched with a pointed object, it draws away. It moves 

A patient investigator watched and described 
the behavior of an amoeba as it went after a 
spherical food particle which had rolled away. 
The drawing shows how the amoeba pursued and 
engulfed the particle of food. 



from the object by sending out tiny projections of cytoplasm, 
which are known as pseudopodia. 

If an amoeba comes in contact with food, it surrounds the 
particles. If touched with wires carrying an electrical charge, it 
rolls itself up into a ball as if shocked. It shows no activity at 
freezing temperature, and it evidences the greatest activity at a 
temperature of about 85° F. It will become spherical, hard, and 
lifeless in very hot water. If a beam of light is directed toward 
one side, the amoeba will move away from the light and toward 
the darkened portion. If a grain of sugar is placed in a drop 
of water, the amoeba will move toward the sugar ; if a grain of 
salt is placed there, it will move away. If, with a very fine 
pipette, a chemical is injected into the amoeba's cytoplasm, the 
animal is able to sever off almost immediately that part of the 
cytoplasm and will move from the rejected part as quickly as 
possible. Recently, Dr. R. H. Chambers has developed methods 
of micro-dissection. By means of a microscope and a set of tiny 
dissection instruments and capillary pipettes he can dissect or 
inject chemicals in or near specimens while they are mounted under 
the microscope. 

The responses or activities of the amoeba called forth by stimuli, 
are tropisms (tropos — a turning) . These responses may be toward 

When the amoeba reaches its maximum size, the nucleus elongates and divides into two nuclei. 
The animal constricts and breaks apart into two daughter cells, each with one nucleus. 

the stimulus, in which case the tropism is called a positive tropism 
and designated by a plus sign ( + tropism). If the resulting ac- 
tivity is a motion away from the stimulus, the tropism is con- 



sidered negative and is represented by a minus sign ( — tropism). 
The different tropisms are named in terms of the stimulus to 
which the organism is reacting. Listed below are the tropisms 

shown by the amoeba. 

Photo tropism — reaction to light. 
Chemotropism — reaction to 

Thigmotropism — reaction to 
touch or contact. 

Thermotropism — reaction to 

Galvanotropism — reaction to 
electric current. 

These reactions are largely pro- 
tective. As a result of tropisms 
the amoeba often escapes unfavor- 
able conditions and gets into an 
environment where the conditions 
are favorable for its life and ac- 

Locomotion. By means of its 
pseudopodia, the amoeba " walks" 
from place to place. It sends out 
a stream of protoplasm in one 
direction. Gradually the rest of the cytoplasm carrying the 
nucleus flows into it ; and again a thin stream is sent out. Thus 
the organism moves. By means of the function of locomotion it 
can get food and escape unfavorable conditions. 

Problem. Study of a Paramecium. 

Place some hay in a beaker of distilled water. Heat in order to soften the 
hay. Let the material stand two or three weeks. The addition of a little 
thyroid extract will usually promote the multiplication and growth of the 
organisms present. This is a Paramecium culture. 

When the amoeba is viewed from the 
side, pseudopodia may be seen to ex- 
tend which result in movements like 


I. Take a drop of the infusion, place it on a slide and cover with a cover 
glass. The microorganisms called Paramecia should be present. 

A. Describe the cellular structure of a Paramecium. 

B. How does its movement differ from that of the amoeba ? 

C. What proof have you that the Paramecium is cylindrical and not flat ? 

D. Describe the shape of a Paramecium. The end that goes forward 
most of the time is called the anterior end. The opposite end is the pos- 
terior end. Describe the shape of the anterior and posterior ends. 

II. Put a few threads of cotton or some finely shredded lens paper on a 
glass slide. Place on this a drop of the Paramecium culture and focus under 
the low power. 

A. Describe the appearance of the threads of cotton under the microscope. 
What effect do the threads of cotton seem to have on the movement of 
the Paramecium ? 

B. Note the furrow in one side of the animal. This is called the groove. 
At the base of the groove is a mouth, and the cylindrical structure below 
is the gullet. 

C. Look closely at the plasma membrane. The structures that you 
should observe there, are projections of protoplasm and are called cilia. 
Describe any movements of the cilia. Suggest a function of the cilia. 

D. The groove and gullet are also lined with cilia. Suggest a function 
for these cilia. 

E. At either end of the Paramecium you will see a small clear bubble. 
Watch each bubble form, grow larger, and burst. These are the contractile 

III. Stain the Paramecium with dilute iodine and mount under the low and 
high power. What evidence of ectoplasm and endoplasm can be seen? De- 
scribe a difference between these two kinds of protoplasm. 

IV. Take a new culture and add a small amount of blue fountain pen ink 
to it, and again put a few threads of cotton on it. 

A. Focus under the high power. Observe the long hairlike structures 
that are thrown out. These are protective structures of offense and defense 
called trichocysts. 

B. Observe the two nuclei. The larger nucleus is called the macro- 
nucleus (makros — large) and the smaller, the micronucleus (mikros — 
small). It may be necessary to stain the specimen with iodine to see these. 

C. Draw a Paramecium three inches long and label all the structures 

D. Write a brief description of the Paramecium. 



The physiological functions of the Paramecium are somewhat 
more complex than those of the amoeba because of the increasing 
complexity of structure. 

Nutrition. Bacteria and any other tiny plants or protozoa that 
are small enough are swept by the current created by the cilia 

into the oral groove. These 
are driven through the gul- 
let, where they are made 
into a food ball and dis- 
charged into the cytoplasm 
of the cell. The food ball 
is carried around as a vac- 
uole by the streaming cyto- 
plasm. The processes of 
digestion, circulation, as- 
similation, growth, and res- 
piration in the animal are 
similar to those described 
for the amoeba. As the 
food is gradually digested, 
any material that cannot be 
digested is collected at a 
certain small area of the 
plasma membrane in the 
posterior end of the animal. 
The membrane breaks at 
regular intervals to throw 
off the solid food wastes. 
This mechanism is called 
the anal opening. Because 
the wall always breaks in 
the same region to let out the solid material, it is frequently called 
a weak spot. The wastes, carbon dioxide, water, and urea, formed 



. jp«lliole> 


oral groove. 

^oo*3L vaduole* 

v. corn. o. I. 


Note in this diagram the structures that you were 
unable to see in your microscopic study of the Para- 



in the oxidation process, are collected by tiny radiating canals 
and emptied into a central contractile vacuole at each end of the 
organism. When these vacuoles have attained a certain size, the 
cytoplasm . surrounding them contracts and discharges the wastes 
through the cell membrane. The contractile vacuole is constantly 
filling and discharging. 

Locomotion. Cytoplasmic structures called cilia project through 
the cell membrane, and, by rapidly lashing back and forth, propel 
the animal through the water. The cilia are ar- 
ranged in rows all over the body. All the cilia in 
a row beat at the same time. If, with a needle, 
the thread of cytoplasm which controls the beating 
of a row of cilia be cut, the entire row will cease to 
beat and remains paralyzed. Due to the more 
rapid beating of the cilia in the groove, the animal 
rotates and proceeds in a spiral rather than a 
straight path. It usually progresses with the blunt 
or anterior end forward, but can reverse its cilia 
and travel equally well with the pointed end for- 
ward. Such a reversion often takes place when it 
meets an obstacle. If confined in close quarters, 
the Paramecium can pass through small openings 
due to the elasticity of its body. 

Reproduction. Reproduction occurs by fission, 
as in amoeba. Each of the two nuclei divides and 
each daughter cell contains a macronucleus and 
micronucleus. A new groove and gullet are formed 
in one of the cells and two new contractile vacu- 
oles appear. When cell division or binary fission goes on indefi- 
nitely, the cells sometimes lose their vitality. When this happens 
they become smaller, and, in some cases, distorted. Under such 
conditions, two Paramecia come together. The cell membranes 
are dissolved at the point of contact and a bridge of cytoplasm 

A Paramecium 
reaches a maximum 
size. The two nu- 
clei elongate, a con- 
striction appears, 
and the two daugh- 
ter cells split apart. 
This is reproduc- 
tion by fission. 


is formed. The macronuclei disappear and the micronucleus goes 
through a series of complicated divisions. Finally one part of the 
nucleus of each cell passes over the cytoplasmic bridge and unites 
with a part of the micronucleus in the opposite cell. The animals 
then separate and there is a reorganization of parts to restore the 
structure to the normal state. This exchange and union of nuclei 
is called conjugation. The process seems to give the Paramecia 
renewed vigor and vitality. The cells may now go on dividing for 
hundreds of generations before conjugation again takes place. 

It has been shown by one scientist that the lowered vitality of 
a colony of certain Paramecia may be caused by the 1 surrounding 
media of their environment. If this becomes concentrated with 
wastes or materials that are unfavorable, conjugation may occur. 
On the other hand, if careful control is kept of this material in which 
the creatures live, and if abundant food is supplied and wastes 
removed, certain Paramecia will divide generation after generation 
without resorting to conjugation. L. L. Woodruff, a professor at 
Yale University, has kept a strain of Paramecia active for several 
years. Thousands of generations have been produced from the 
creature with which he started. By exercising great care to make 

the surroundings most health- 
ful for Paramecia, he has pro- 
Pellicle - duced these thousands of gen- 
erations without having them 
conjugate or die. This biolo- 
SSoagulcctecl Protoplasm, gist believes that if conditions 
ohoi is added to a Paramecium the proto- are carefully safeguarded and 

plasm is dehydrated, the strands of cytoplasm, controlled, these tinV masses of 
cilia, are pulled through the cell membrane or " 
pellicle leaving the rows of openings in the protoplasm known as Para- 
pellicle. r . . 

mecia will live forever. 
Irritability. The reaction of Paramecia to external stimuli is 
much the same as in amoebas. Because of their cilia, they can 
respond more quickly toward or away from stimuli. They have a 



special set of protective structures called trichocysts. Each one 
of these structures consists of a pocket fitted with a long strand of 
cytoplasm which is thrown out when danger is near. This strand 
secretes a poisonous substance. 
The whole mechanism acts as 
a protection. A worm, much 
larger than a Paramecium, as 
it thrashes about, might injure 
the Paramecium. To protect 
itself, the Paramecium dis- 
charges trichocysts which will 
pierce or poison the enemy so 
that it will become inactive. 

Protoplasm is specialized. 
The specialization of protoplasm 
in Paramecium is a step toward 
the specialized organs for defi- 
nite functions found in higher 
animals. The protoplasm of 
the amoeba shows very little differentiation. Pseudopodia may be 
thrown out from the body at any place. Food may be taken in and 
water given off from any part of the body. The only specialized 
protoplasm of the amoeba seems to be the nucleus and the plasma 
membrane around the contractile vacuole. In the Paramecium 
there are definite parts of cytoplasm specialized to form cilia. 
These are constant structures used for locomotion and for propel- 
ling food into the mouth. There is a definite part of the cytoplasm 
forming the groove, mouth, and gullet. Food is taken in through 
these structures. The two nuclei, the contractile vacuoles, cell 
membrane, and anal canal are all fitted or adapted to the functions 
they have to perform. The Paramecium is one of the simplest 
organisms to show definite adaptations to function. Physiological 
division of labor is accomplished by specialized protoplasm. 


If a small drop of fountain pen ink is put on 
a Paramecium, the animal throws out long 
protoplasmic structures, trichocysts. These A 
threads usually secrete a substance that stuns '*- 
an enemy or the prey. 


Simple animals are very similar to simple plants in structure and 
function. The main differences are that animals have the function 
of locomotion, and are adapted to perform this function. Very few 
plants have the power of locomotion. Green plants manufacture 
their own food by means of their chlorophyll, and do not have to 
seek food as most animals do. In addition to the plasma mem- 
brane, there is a protective wall in the plant cells made of a non- 
living material, cellulose. This is missing in animal cells. Amoebas 
are bounded by the plasma membrane only. 

A cell, either plant or animal, has been shown to be a tiny mass 
of protoplasm, generally having a nucleus and having a boundary, 
a cell wall, or an animal membrane. The cell theory as first stated 
by Schleiden and Schwann has been checked by many scientists 
over a long period of years. To-day, it is no longer considered 
a theory but is accepted, somewhat modified, as a doctrine. 
Among other things this theory states that the cell is the unit of 
structure and of function and that all plants and animals are 
made up of cells and cell products. 


1. Name the forms of energy needed by the amoeba or Para- 

2. Classify the physiological functions into nutritive, adaptive, and 
reproductive. Give the functions of each class. 

3. Why is digestion necessary in animals ; in plants ? 

4. What is the main difference in the nutrition of a plant and 
animal ? 

5. Discuss some positive and negative examples of tropisms. 

6. In outline form, compare the structure and function of a one- 
celled plant and a one-celled animal. 

7. Discuss the importance of chlorophyll to animals. 

8. What is meant by physiological division of labor and speciali- 
zation of protoplasm ? 

9. Make a library report on the economic importance of protozoa. 





When cells divide 




the surface area increases. 

What is the nature of protoplasm? What progress has been made 
in the building of protoplasm in the laboratory? Are the functions of 
the cell related to the functions of the organism in any specific way? 

All living things are made of cells. The cell is the unit of struc- 
ture of the. Protozoa. Higher forms of organisms are composed of 
many cells. It is impossible to discuss the functions of higher 
organisms without referring to the cell in some detail, for it is 
really the cells of the organism that perform these functions. Cells 
vary in shape, size, and structure, but they are all alike in consist- 
ing of a mass of protoplasm usually containing a nucleus, and 
always surrounded by a plasma membrane. A plant cell is in- 
closed in a cell wall which usually consists of cellulose, a form of 
carbohydrate. Cells are either in a state of division, or, if not 
actively dividing, are said to be in a state of rest. When in the so- 
called state of rest, activities other than cell division are being 
carried on in the cell. 

The nature of the cell and its make up. So complex is the cell 
and so much has been written about it that there is now a whole 
branch of biology, cytology, concerned with cell investigations. 

Cytologists differ as to the detailed structure of protoplasm. 
Some think it is composed of an extremely minute network of fibers, 
similar in appearance to a sponge, inclosing a liquid. This is 




called the reticular theory. A second group of scientists believes 
that protoplasm is similar to a mass of bubbles, like soapsuds or a 
froth. This group thinks the so-called fibers are only the delicate 




The structure of protoplasm has not been satisfactorily determined. It has been described in 
various ways and represented as in the above diagrams. 

lines separating the bubbles from each other. This theory is called 
the alveolar or the foam theory. A third group thinks that proto- 
plasm is an infinite number of very small, living, moving granules 
arranged in lines resembling fibers. These fibers, differently ar- 
ranged, make various figures This is the granular theory. All 
biological problems are centered in the cell, including the manu- 
facture and use of food, and an understanding of the nature of 
and the control of problems of heredity. Such problems shall 
never be satisfactorily settled until more knowledge of the work 
of the cell is gained. 

Many investigators are now trying to solve cell problems. Con- 
sider the work of Alexis Carrell, the French surgeon. For years 
he and his assistants have been working at Rockefeller Institute, 
New York city, trying to develop various cells outside of a living 
organism. For sixteen years he has kept cells of a chicken embryo 
actively growing. He has also succeeded in getting other living 
cells to grow under controlled circumstances. He has been able to 
use some of these cultivated cells to try out the effects of various 
antiseptics. It is possible that cultivated tissues will be of great 
value in operations of skin grafting. Growing tissues for this 
purpose is only one small part of the work now being done by 
Carrell. He has transplanted whole organs from one animal to 


another and succeeded in having them grow and function in the 
second animal. His work on antiseptics, during the World War, 
was invaluable. It seemed almost impossible to keep wounds free 
from contaminating germs which destroyed the cells. He and 
Dakin prepared and introduced an antiseptic, Dakin solution, for 
treating wounds. This solution, which did not injure the tissue, 
saved many soldiers from gangrene and other infections. 

The problem of heredity which involves an understanding of 
certain cells is now being studied by many scientists. It is a well 
known fact that certain physical and mental traits are transmitted 
from parent to offspring through a granular material, chromatin, 
found in the nucleus of the germ cells. This chromatin combines 
to form the structures, chromosomes, which carry and transmit 
certain character determiners. Experiments are now being made 
to find out exactly what characters are inherited, and the amount 
of the hereditary-bearing substance. Why has a certain individual 
one ability, while another in the same family lacks this ability? 
Scientists, including T. H. Morgan, W. J. V. Osterhout, E. B. 
Wilson, and R. H. Chambers, are working on this problem at the 
present time. 

Characteristics of protoplasm. Protoplasm is being studied by 
many biologists from four different viewpoints. 

Physically — it is a constantly streaming, colorless, slimy, semi- 
liquid substance similar to the white of an egg. It is a colloid. 
By that we mean it is a mass of tiny solid particles suspended 
in a liquid. It will not pass through a parchment membrane. 

Chemically — it is a very complex unstable mass made of pro- 
teins and inorganic salts associated with a large amount of water 
and frequently containing carbohydrates and fats. 

Structurally — it is variable. Sometimes it appears purely gran- 
ular, other times fibrillar or threadlike, and again it may resemble 
a mass of foam or bubbles. It varies according to the activity 
and individual nature of the cell. 



Physiologically — it lives, moves, reproduces, and dies. If kept 
under proper conditions, such as Woodruff and Carrell kept it in 

their experiments, protoplasm seems 
to be able to live indefinitely. 

Dr. Calkins, of Columbia Uni- 
versity, has performed many experi- 
ments on certain cells to show 
the importance of the presence of 
nuclear material. In one experi- 
ment he used Uronychia, a one- 
celled animal. Like its relative, 
Paramecium, this creature has two 
nuclei, a macronucleus and a micro- 
nucleus. The protozoologist divided the tiny creature into two 
fragments, each having an equal part of the macronucleus and 
micronucleus. Both parts healed. Both grew and reproduced. 
Then he divided a second organism unequally so that the smaller 


An amoeba was cut apart, one portion 
bearing the nucleus. Both fragments 
healed, both continued to move, but the 
one without a nucleus soon slowed down, 
came to rest, and died. The nucleated 
portion grew and became a normal 

A Stentor, relative of Paramecium, was 
cut in three parts. Each fragment had a 
part of the nucleus. Each grew and re- 
generated missing parts, resulting in three 
new and complete animals. 

A Stylonychia was cut so that only one of 
three fragments contained nuclear material. 
All three swam about for a time but only the 
portion bearing the nuclear material regen- 
erated lost parts, grew and reproduced. 

part had little macronuclear material and no micronucleus. It 
took in little food, grew, but did not reproduce. It soon died. 
The larger portion of the animal, containing most of the macro- 


nucleus and the micronucleus, healed, took in food, grew, repro- 
duced, and was soon a normal animal. 

Many other similar experiments have been conducted, the results 
of which indicate that the macronucleus is an essential factor in the 
metabolism, growth, and regeneration of the organism. The micro- 
nucleus has to do with reproduction. 

The protoplasm may be divided into cytoplasm and nucleo- 

Structures found in cytoplasm Structures found in nucleoplasm 

Cell wall (plant cells only) Nuclear membrane 

Plasma membrane Nucleolus 

Vacuole Chromatin granules 

Cell sap Linin network 

Vacuolar membrane Nuclear sap 

Chloroplasts (in some cells) 

Starch grains 

Crystals (protein, urea) 

Centrosome (animal cells chiefly) 

The functions of the different parts of protoplasm. The nucleus 
consists of very dense protoplasm bounded by a delicate membrane. 
It may lie anywhere in the cytoplasm of the cell. In fact, it is 
constantly being carried to different parts of the cell by the stream- 
ing movements of the cytoplasm. It generally contains a minute 
spherical body, the nucleolus. Sometimes there are several nucleoli 
in one cell. The exact function of the nucleolus is not known. 

A typical resting nucleus shows many particles called chromatin 
granules. These are enmeshed in a network called linin. The 
chromatin granules are believed to be the carriers of hereditary 
character determiners; such as, the color of a person's eyes, his 
disposition, his height, or his artistic ability. These particles are 
able to absorb certain stains more readily than the rest of the 
materials found in the cell. 

The nucleus controls the work of the cell. It is the center of all 
the physiological activities of the cell; such as, nutrition, respiration, 




cell ^rctll 



A plant cell has a cell wall. When viewed 
through a microscope large vacuoles are generally 
seen in the cytoplasm. 

growth, and reproduction. A cell without a nucleus (the nucleus 
having been removed with a tiny knife) will not live. Without a 
nucleus, although food is present, the cell cannot take in food, nor 

use food, and its respiration 
becomes greatly reduced. 

The cytoplasm is the living 
material of the cell, surround- 
ing the nucleus. It is semi- 
fluid, less dense than the 
nucleoplasm, and is always 
in motion throughout the cell. 
The cell wall is found as 
an additional bounding layer 
around plant cells. It is com- 
posed of a substance, cellulose, 
which has the elements found 
in starch ; namely, carbon, hydrogen, and oxygen. Cytoplasmic 
threads penetrate into the cell wall, and cause it to grow in thick- 
ness by depositing woody material. As the cell gets older, more 
and more woody material is deposited. Within this thickened 
wall of the plant cell is the plasma membrane. In the animal cell 
the plasma membrane is the only bounding layer; it lacks the 
material which makes up the plant cell wall. The plasma mem- 
brane is a very delicate layer of dense cytoplasm and has three 
functions in plants and animals. It regulates osmosis by permit- 
ting the entrance of needed materials. It determines the shape or 
form of the cell. It affords protection against loss of water. 

A vacuole is a space in a plant cell which becomes filled with a 
liquid called the cell sap. The cell sap contains a little dissolved 
sugar, mineral salts, crystals (waste and storage products of the 
plant cell), and a great deal of water. The presence of a vacuole 
helps the plant cell to swell up and become very large even 
though only a small amount of cytoplasm is present. This cyto- 



plasm becomes stretched into a thin layer around the vacuole. 
The vacuole is bounded by a delicate layer of cytoplasm, J;he 
vacuolar membrane. Some animal cells possess vacuoles similar 
to the food and water vacuoles of the protozoans, and contractile 
vacuoles for the excretion of nitrogenous wastes. 

A chloroplast is a small mass of cytoplasm, colored green by 
the chlorophyll pigment. The cell aided by this chlorophyll in the 
presence of sunlight is able to manufacture raw materials into the 
food necessary to build protoplasm. 

The centrosomes are the foci for the starlike formations ap- 
pearing like fibers of cytoplasm. These seem to be of great 
importance in the division of the animal cell. 

The sum total of all the functions of the cell is called metabolism. 
It refers to the physiological activities of all living protoplasm. 
There are two kinds of metabolic activity ; anabolism and katab- 
olism. When the physiological activities tend to build up proto- 
plasm, they are termed anabolic. Two examples of anabolic 

celt „ 








Compare this animal cell with the plant cell on the previous page. 

activities are starch making and assimilation. When these pro- 
cesses tend to break down protoplasm, they are katabolic. An 
example of a katabolic process is the oxidation of food. Both types 



of processes are essential to the work of the cell and depend upon 
each other. The anabolic activities are concerned chiefly with 
nutrition and the katabolic, with energy release. For example, 
in order to perform the anabolic functions of assimilation', the 
cell is dependent on the energy derived from the katabolic func- 
tion of respiration. 














Cell division. When a cell is not at rest, it is in a state of divi- 
sion. There are two methods of division: 1. Direct division — 
also called amitosis {a — without; mitos — thread), and 2. in- 
direct division or mitosis. In amitosis, direct division, the nu- 
cleus simply pinches in half and becomes separated into two 
daughter nuclei. The cytoplasm sometimes cleaves and a part 
goes with each nucleus. * This sort of division takes place only in 
cells which are very active and need very many nuclei in the work 
they are doing. Amitosis may also occur when cells have been 
very active, and the nucleus, becoming exhausted, multiplies 
rapidly by breaking into fragments. 

Mitosis or indirect cell division. Mitosis is a very compli- 
cated process when compared with amitosis. The nucleus lives a 
very long time in an active and young cell, and will divide a great 
many times. Each time the nucleus divides, the entire cell di- 
vides, forming two new cells. Each cell will have exactly the 



same characteristics possessed by the original cell. This equal 
inheritance is made possible by the dividing of every chromatin 

1 2 3f 4r 



Mitosis of an animal cell, Ascaris egg. Follow the stages shown in the diagram with the 
description given in the text. 

granule into two parts, so that each cell will possess the same 
number. In order to bring about equal splitting, several distinct 
stages are gone through. This process takes place in all plant 
and animal cells, from the protozoans and algae to the cells of the 
largest trees and the most complex animal, man. 

In many animal cells, the first sign of mitotic activity is the 
separation of the centrosome into two parts connected by delicate 
fibers. Around each center, groups of fibers radiate, causing the 
structures to look like stars. Hence, they are called asters and 
the radiating rays are known as astral rays. 

The centrosomes move further apart around the nuclear mem- 
brane and the spindle threads become longer. At the same time 
the chromatin granules become arranged in the form of separate 
threads or a continuous coiled thread, the spireme. 




The spireme breaks up into a number of parts called chromosomes. 
Each plant or animal cell seems to have a definite number of these. 

In the cells of human beings, 
the spireme breaks up into 
forty-eight chromosomes. In 
the onion cell, there are sixteen. 
In a certain little fruit fly, 
there are only eight. These 
numbers are always constant 
for a particular species. Four 
chromosomes are shown in the 
diagrams (page 61) illustrat- 
ing mitosis of an animal cell. 
The asters separate more 
Photomicrograph of a section of a growing and more widely causing the 

root tip of an onion. How many different stages £U~„~ U~+ w ~~.^ +U~ + U~ 

of ceil division can you identify? fibers between them to be- 

come longer and to assume 
a spindlelike shape. Finally they reach the opposite sides of 
the nucleus. The chromosomes are' now drawn into the central 
part of the spindle forming a ring around it, in a plane called 
the equatorial plate. All of these changes are a part of the 
prophase stage (beginning) of mitosis. The prophase ends with 
the chromosomes arranged on the spindle in the equatorial plate. 
Each chromosome now splits lengthwise into exactly two similar 
parts. The actual splitting of the chromosomes may occur before 
the arrangement at the equatorial plate. Division of the chromo- 
somes has been accomplished. This is the metaphase (middle) 
stage of mitosis. 

The split chromosomes begin to separate and move toward 
the centrosomes or the poles. As they approach their poles the 
chromosomes lose their regularity of outline, and upon reaching 
the poles each group becomes converted into two new nuclei. 
This is the anaphase (approaching the end) stage of mitosis. 



Mitosis ends with the telophase. A new cell wall forms on the 
spindle, midway between the two daughter nuclei. It divides 
the cell into two parts, in each of which a nucleolus now appears. 

Problem. Study of mitosis. Study of pre/pared slides of Ascaris 
under the microscope. 

I. Select a good example of the anaphase stage. 

A. How does the slide differ from the diagrammatic drawings ? 

B. What causes you to identify it as an anaphase stage ? 

II. Identify any other stage of mitosis present in your specimen. 

III. Make an outline drawing of three different cells seen through the micro- 

IV. Alongside of each drawing, copy and label the diagram of the phase 
which most nearly resembles the viewed cell. 

A very similar process takes place in plant cells. Centrosomes 
are lacking. The spindle forms from material which is probably of 

A group of cells of a plant showing various stages in the mitotic division of the cells. Com- 
pare and contrast this series with the diagrams showing mitosis of an animal cell. 



nuclear origin. A cleavage plate through the middle of the cell is 
secreted by the cytoplasm. This divides the cell into two parts. 
There is no constriction here as there was in animal cells. 

Cell theory. The illustration (below) shows some of the men 
who have discovered and made known many interesting facts about 
animal and plant cells, so that we to-day have come to have four 
ideas concerning the cellular structure of all organisms. 

1. The cell is the unit of structure of all living plants and animals. 

2. The cell is the unit of all physiological functions of living plants 
and animals. It is the cell that breathes, digests food, excretes wastes, 
moves, and performs all the other physiological functions. 

3. The cell embraces all the hereditary qualities of the organism 
within its nuclear membrane. 

4. Plants and animals may consist of single cells. They always 
start with a single cell, and in their early stages of development (em- 
bryo) this cell divides and changes into many cells. 


Hall of Fame for biologists -who worked on cell* 

Century . . 

Country . . 


1. Copy the names and fill in the blank spaces in the above table. 
Check your results with your answer to question 1 on page 33. 
...2, By means of paraffin, soap, clay, or plasticine try to make 
models of a resting cell and some of the stages of mitosis. . . , '-. 


3. Name the structures common to both plant and animal cells. 

4. List the living and nonliving structures in a plant cell. 

5. What parts of a cell are most active during mitosis ? 

6. In what kinds of cells is amitosis carried on ? Why ? 

7. Draw, a characteristic stage of each phase of mitosis. 

8. Why is it that every cell in an organism has chromosomes of the 
same nature found in every other cell ? 

9. Discuss the cell as the unit of structure ; the unit of function. 
10. Discuss the importance of the cell in the development of the 


Supplementary Reading 

Gager, C. S., General Botany (P. Blakiston's Son & Co.). 

Locy, W. A., Biology and Its Makers (Henry Holt & Co.). 

Wilson, Edmund B., Cell in Development and Heredity (The Macmillan Co.). 



Photomicrograph of corn 

Photomicrograph of woody 

What is meant by physiological division of labor? Does each plant 
cell of a higher plant live independently or are the cells dependent 
on each other? Why can one type of cell perform a function better 
than another type? What advantages have higher plants over simpler? 

Social division of labor. In any civilized community certain 
individuals perform one type of labor more efficiently than others. 
There are seamstresses to make clothes, shoemakers to make shoes, 
milliners to make hats, engineers to run trains, clerks to perform 
clerical work, typists to typewrite, and numerous other specialists, 
each performing a specific work. The people who are most suc- 
cessful are those who are particularly fitted or adapted for their 
positions, either through special training, natural talent, or size. 
More efficient work is accomplished in less time when it is divided 
among specialists than if each man had to do all the work himself. 
Similar to the division of labor among people in the industrial 
world, there are in our bodies numerous activities that are car- 
ried on by various structures especially adapted for that work. 

Physiological division of labor. There is physiological division 
of labor in all plants and animals. The amoeba, Paramecium, 
Pleurococcus, Spirogyra, and countless other plants and animals 
are sufficient each in itself. Each with its one cell, by means of 
specialized protoplasm, performs all the activities and processes 



necessary for living. These organisms, however, live very simply. 
The many-celled plants and animals are much more complex. 
They consist of a variety of cells. Differentiation of cells and 
greater specialization of function are shown in these. Whenever 
there is a collection of similar cells in higher organisms, it is known 
as a tissue. 

Problem. Study of the lower epidermis of a leaf. 
Peal off the under surface of a geranium leaf. Mount it under the low 
power of the microscope. 

I. Describe the shape, color, and structure of the different types of cells 
in the epidermis. 

A. Epidermal cells have unusually thick walls. Remembering that the 
epidermis is the outer layer of the leaf, suggest a function of the thick- 
walled cells. 

II. Note the small holes between the oval-shaped cells. Each of these is a 
stoma (from a Greek word meaning mouth or opening). Suggest a function for 
these openings or stomata. 

A. The oval-shaped cells, called guard cells, are so constructed as to 
cause the opening and closing of the stomata. 

B. Draw and label the lower epidermis of a leaf. 

C. Describe briefly the functions of the cells and the adaptations of the 
cells to their functions. 

Problem. Study of a cross section of the same leaf. 
Place a leaf between two pieces of cork and cut through the cork with a 
sharp razor blade. 

I. Describe the general arrangement of the cells in the upper epidermis, 
middle area, and lower epidermis of the leaf, as seen in the cross section. 

II. Note the upper colorless epidermal cells bearing hair-like structures. 
Suggest a use for these cells. 

III. Note the regular arrangement of the cells immediately under the 
upper epidermis. This layer is called the 'palisade layer or tissue. How 
are the cells in the palisade layer arranged so as to secure sunlight ? 

IV. Observe the loose arrangement of the cells under the palisade tissue. 
These cells form the spongy layer. 

A. What is the advantage of the air spaces among the green cells? 

B. State a function of the green cells of the leaves. 


V. Observe the side view of the cells in the lower epidermis. Describe the 
appearance of the epidermal cells, guard cells, and stomata. 

VI. Discuss the importance of the translucent character of the epidermal 

VII. What specialization of structure for function is shown in a green leaf ? 
Give at least five examples. 

VIII. Secure two leaves from a rubber plant. Coat the upper epidermis of 
one and the lower epidermis of the other with vaseline. Seal the ends of the 
stems with vaseline. Keep them in a cool place for several days. 

A. State your observations. 

B. . Suggest a second use for the stomata. 

Problem. Study of the vascular and supporting tissues in a leaf. 

Break off a narcissus leaf and separate some tissues from the broken end. 
Mount on a glass slide. 

I. Observe some of the cells with spiral thickenings on the walls. These 
are tracheids (xylem). In order to keep open the passageway of the tubes 
formed by these cells, spiral thickenings of wood form on the wall. Originally, 
there were cross walls where one cell ended and another began, but the parti- 
tions have been absorbed, leaving an uninterrupted canal. Water travels 
up through these tracheids. 

II. There are other cells with sievelike plates at regular intervals. These 
are the sieve tubes (phloem). Through these structures materials pass down 
the plant from the leaves to the roots. 

A. Trace a material that travels from leaves to roots. 

B. Why do materials tend to pass more quickly down than up ? 

C. What is a possible advantage of the sievelike cross walls in the 
sieve tubes? Each sieve tube is a single row of elongated cells placed 
end to end and the thickened end walls of these cells have numerous 

III. There are also supporting tissues called wood fibers that have very thick 
walls of cellulose. Some of them consist entirely of cellulose and compose the 
supporting structure in a plant. 

IV. Place the roots of a complete narcissus plant or any other young plant 
in red ink or eosin in order to show the continuous pathway from roots to leaves. 

A . What evidence of the passage of fluids do you observe ? 

B. Trace the liquid that travels up in a plant from the point of en- 
trance to the cells that use it. . " j 

V. Draw and label as many of the tissues as you have observed; 



VI. In a paragraph, discuss the functions of the vascular or conducting and 
supporting systems of a plant, including the adaptations or specializations for 
various functions. 

upper surface lower surface 

Most leaves are covered with a layer or layers of thick-walled cells lacking chlorophyll. 
The lower surface of most leaves bears certain paired cells containing chloroplasts. These 
cells permit the passage of substances in and out the leaf. They are the guard cells. 

Specialization in higher plants. Higher plants perform all 
the physiological functions necessary for life. Each individual 
cell performs many of these same functions, but at the same time 
each cell is adapted to perform 

one function better than others. 
Absorption of water and minerals 
is performed by special epidermal 
cells called root hairs, found on 
the roots. These cells are long 
and slender and grow among the 
particles of soil. The water and 
mineral matter pass through the 
root hairs, then through other 
root cells until they reach the 
ducts (xylem) near the center of 
the root. By means of capillary 
action, evaporation of water from 
the leaves, and the pressure of 
other fluids following, the water 
rises in the spirally-thickened 


wall of a 
guaro. cell 

nucleus of a 
guard, cell 

£ ^gtiatSlcell 

A surface view and cross section of the 
specialized epidermal cells which make a 
passageway, to the air spaces within the leaf. 



The fibrovascular bundles are made up of different types of woody cells, some pitted, others 
ribbed and still others strengthened by spiral or circular thickenings on the walls. 

and pitted ducts until it reaches the chorophyll-bearing or green 
cells, particularly those in the middle part of the leaf. The green 
cells absorb the water from the tracheids. Here, again, absorp- 
tion is a cell function. Oxygen for respiration and carbon diox- 
ide for photosynthesis diffuse through the stomata in the lower 
epidermis of the leaves, through the air spaces in the middle layer 

of the leaf, and, by means of 
osmosis, pass into the green 
cells. In these green cells, 
photosynthesis, fat manufac- 
ture, and protein manufacture 
take place. These processes 
are considered leaf functions 
because they take place in 
the green cells of the leaves. 
Again the function of the 
organism is really a cell func- 

When greatly magnified, a woody bundle of the Excess food passes into the 

corn stem shows many of the tubes which are the . . . . 

passageways for the food of the plant. Sieve tubes and IS Conveyed 



— >-Foo3l travels 

->:wctt^er gbe 

" V P 

down to especially adapted layers of cells in the stem or in the 
cortex of the root, for storage in the form of starch granules, oil 
globules, and protein crystals. Turnips, parsnips, and radishes are 
used by people for food because of the extra plant food stored 
in them. In the case 
of the potato, the 
extra food is stored in 
an underground stem ; 
in asparagus, sugar 
cane, and rhubarb, it 
is stored in stems 
above the ground. 
When the plant needs 
food, a protease, 
lipase, and amylase 
secreted in the cyto- 
plasm of the cells that 
store food, change the 
stored materials again 
to a soluble form. 
These dissolved foods 
are then distributed 
by means of the ducts. 
Supporting cells are 
usually found in con- 
nection with the ducts 
and sieve tubes. 
These woody fibers 
support the plant. 
Those in the lower part of the plant strengthen the roots and 
help to anchor the plant in the ground. The woody fibers of 
the stems help hold up the leaves and enable them to get sun- 
light which is necessary for photosynthesis. 

There are pathways through which fluids pass up and down 
in plants. Raw materials travel up the stem into the leaves. 
Food manufactured in the leaves travels down to the roots. 



jgUorfa Cells 



In cross section, a certain leaf will show cells 
arranged in an orderly fashion. One part of the 
leaf contains many air spaces through which gases 
are exchanged with the active surrounding cells. 

All cells need energy to 
carry on their work. Each 
cell takes in oxygen, oxi- 
dizes the food distributed 
to it, and gives off carbon 
dioxide and some water. 
'These materials may be 
distributed either through 
the vascular system or by 
passing from cell to cell. 
The entire plant grows by 
the growth and division 
of the individual cells. Reproduction of the plant is too compli- 
cated to discuss here, but it will be found later that it, too, is due 
to the division of certain cells. 

In this chapter, the shape of plant cells has been considered. 
It is by their shape, organic nature, and arrangement that they are 
fitted to perform certain functions. Each cell of higher plants 
contains the structures discussed in a resting plant cell. It is by 
the coordination of all these cells that the entire plant functions. 


1. Make an outline of the specializations in higher plants, using the 
headings (a) name of tissue, (b) function, (c) adaptation to function. 

2. Name the structure in a higher plant corresponding in function 
to each structure observed in a cell of Spirogyra. 

Supplementary Readings 

Coulter, Barnes, and Cowles, A Textbook of Botany (American Book Co.), 

Vol. I. 
Holman, R. M., and Robbins, W. W., A Textbook of General Botany (John 

Wiley & Sons, Inc.). 
Gager, C. S., General Botany (Blakiston's Son & Co.). 


Bone cells build skeletons. 

Skeletons of fish and frog. 

How can the minute structure of the body be investigated? How is 
division of labor performed by the human body t What are bone and 
cartilage f How are the cells in a multicellular organism held together f 

If a thin slice of any portion of the human body is examined 
microscopically, it will be found to consist of a mosaic of minute 
units called cells. It will be further found that no cell conforms to 
the diagram of the typical cell. There are masses of similar cells 
that build tissues, and these tissues build more complex structures 
called organs. Each organ has a special duty or function. In 
the human body there is greater specialization than in the higher 
plant. Each tissue or group of cells is adapted to perform a par- 
ticular physiological function. At the same time, all the functions 
necessary for life are carried on within each cell. 

The cell the unit of structure. Any function of an organism 
must be considered in relation to the function of tissues or of cells, 
because it is the individual cell that does the work. Fundamen- 
tally, each cell possesses the complete apparatus for life. Tissues 
can be compared to collections of single-celled organisms in that 
they perform most of the functions that the one-celled animals 
carry on ; but each group of tissue cells is fitted by shape, structure, 
location, or chemical powers to perform special functions necessary 
to the life of the complete organism of which it is a part. There- 

WH. FITZ. AD. BIO. — 6 73 



Scdcnnotnaer cells of 'Sfclvox, ot t 
Skin cells colonial protoyxm 

cells from. « 

In most organisms, cells are not separate and distinct 
units, but are joined to one another by delicate strands of 

fore, it may be said that all of the tissue cells work together to 
accomplish the life processes of the organism. This is brought 

about by differentia- 
tion of structure for 
division of labor. 

The cells of multi- 
cellular animals and 
plants are not isolated 
individuals, but are 
probably held together 
by some kind of cyto- 
plasmic continuity. 
Biologists have found in certain cases, and have reason to believe 
that in most cases, slender cytoplasmic bridges connect the various 
cells. This gives direct continuity to the cytoplasm throughout 
the entire organism, and probably enables the 
organism to act as a unit even though it is 
composed of millions of different cells. 

Many cells of the body deposit intercellular 
materials, which give additional structural 
strength. The amount of the deposit varies. 
Bone cells deposit a large amount of such 
material; epithelium produces a very small 
amount. Protoplasm is the foundation sub- 
stance of cells. Groups of similar cells with 
their intercellular materials make up tissues. 
When tissues are grouped to make a larger 
structure to perform a certain function, that 
structure is called an organ. Thus, the en- 
tire plant or animal organism is a combi- 
nation of organs built of tissues, which in turn are built of cells. 
The tissues of the human body may be classified into epithelial, 
supporting or connective, muscular, blood, and nervous. 


=81-311 311 




The cell is the unit of 
structure and function in 
every organism. 



■»*■■ *^ riill 


Problem. Study of certain epithelial cells. 

Take a toothpick and gently rub the inside of the cheek and gums. Mount 
the material from the toothpick in water and add just enough fountain penink 
to give a slightly-bluish tint to the water. Study with the low and high mag- 

I. Describe the shape, color, relative size, and structure of the cells. 

II. Draw a group of epithelial cells at least five times larger than they 

III. Write a brief description of epithelial cells. 

Epithelial tissue. Epithelial 
cells cover and line the organs 
of the body. They make very 
little intercellular material. Their 
function is protection and secre- 
tion. They may protect certain 
organs against invasion of foreign 
material, or, by means of their 
moist secretion, guard other or- 
gans against friction. The epi- 
thelial cells that line the nose, 
throat, digestive system, and air 
tubes or respiratory system make 
up the tissue called mucous mem- 
brane. (A membrane is a very 
thin structure consisting of a 
single layer or a few layers of 
cells.) The cells lining the wind- 
pipe have tiny projections of 
protoplasm called cilia. Germs 


i '(gyp 





Cubicocl Columtvocr 

StrcctifieSt OiliocteSL 

Epithelial cells vary in shape. They may 
appear as a single layer or groups of layers 
of flattened, cubelike, or columnar units. 

The cheeks are lined with squamous epi- 

are pushed Or moved back into - thelialcells; the respiratory tract with cili- 
r # ated, epithelial cells. 

the throat by means of this brush- 
like arrangement. They work very much like the cilia of the 
Paramecium. Because of the mucous epithelium in the alimentary 
canal, food slips easily through the tube with no friction. In addi- 




TL" " 

,*> . 

secreting ceBs a simple a tubular 
2globletrc*Hs multi^kdccr gWa 

On olv«olai^ 



a compounds, 
alveolar* glajioL 

or cxswvpoxcrCcl ~ 
jpubvxlccr g'lotnol 

tion to mucous cells, there are other epithelial cells in the alimen- 
tary canal adapted for secreting digestive juices. 

The epithelial cells lining the closed cavities of the body com- 
pose structures called serous membranes. The serous membranes 
line blood vessels, cover the lungs, line the chest, cover the 
heart, cover the abdominal organs and line the abdomen. The 

serous membranes that 
cover the lungs are the 
pleurae (pleura — rib) . 
In breathing, when the 
lungs become inflated or 
larger, and compressed or 
smaller, there would be 
friction between the lung 
and the wall of the chest, 
were it not for this moist 
epithelial tissue. If the 
pleurae become inflamed, 
the person is said to have 
pleurisy. If the secretion 
of fluid is interfered with, there is friction between the lungs and 
the. walls of the chest and breathing becomes painful. 

The covering of the heart is the pericardium (peri — around ; 
cardium — heart). This membrane prevents friction between the 
heart and lungs and other organs. The membrane lining the 
abdomen is the peritoneum. Infection or inflammation of the 
peritoneum is known as peritonitis. This condition is sometimes 
brought about when an infection extends from a ruptured appen- 
dix and attacks a part of the peritoneum. Friction among the 
abdominal organs such as stomach, liver, and intestines is avoided 
by the moist epithelial peritoneum. The abdominal organs do 
not float in the abdominal cavity. If they did, jumping or bend- 
ing might throw them out of place. They completely fill the 

Epithelial cells may manufacture secretions. Certain 
cells, globlet cells, are found in the gullet. They give 
out mucin. Groups of epithelial cells often form simple 
or compound glands which give off certain secretions. 


abdominal cavity, and are attached to each other and to the 
walls of the cavity by means of the peritoneum. A portion of 
the peritoneum, called the mesentery, holds the intestines to the 
backbone. If any organ of the abdomen is removed a part of 
the peritoneum must be cut to separate that organ from other 

The outside of the body may be compared with a body cavity 
in that it is covered with epithelial tissue called skin. The outer 
layers of the tissue become flat and horny, and the outermost 
ones are dead. The hair and nails develop from certain skin 

Supporting tissues. These tissues are all alike in that they con- 
nect and support the other tissues of the body. They, in con- 
trast with the epithelial tissues, are noted for the abundance of 
intercellular material. The main supporting tissues are bone, 
cartilage, white fibrous, yellow elastic, and fat or adipose tissue. 

Problem. Study of cross structure of bone. 
Obtain some rib bones of a lamb from the butcher. 

I. Let some of the rib bones stand in a ten-per cent solution of hydrochloric 
acid for at least two weeks. 

A. How does this treated bone differ from ordinary bone in appearance 
and texture ? The acid dissolves out the intercellular deposits of mineral 
matter, leaving only the organic material. 

B. State the importance of mineral matter in the bone. 

II. Burn some rib bones in a very hot flame. 

A. How does the burned bone differ from ordinary bone? Since or- 
ganic material fyurns, the bone cells were destroyed, leaving only the 
intercellular mineral matter. Bone consists of a combination of bone 
cells and intercellular material. This intercellular material is deposited 
by the bone cells. It is mineral matter, largely calcium phosphate and 

B. State the importance of the cells in the bone. 

Secure some shank bones or other long bones from the butcher. Have him 
saw one lengthwise so that the interior of the long bone, including the enlarged 
head, may be studied. 


I. Describe the material covering the enlarged head of the bone. 

A. Is this material (cartilage or gristle) shiny or dull; moist or dry; 
smooth or rough ; tough or soft ? 

II. How does the texture of the bone under the cartilage differ from the 
bone of the shank? 

III. Describe the material filling the space in the center of the bone. This 
is bone marrow and consists largely of fat cells. Compare the marrow in the 
head of the bone with that in the other parts. 

IV. The outer membranous covering of bone is the periosteum (peri — 
around; osteon — bone). 

Problem. Study of microscopic structure of bone. 

I. Mount a prepared slide of bone cells under the microscope. Note the 
spiderlike, irregular cells arranged around a central space. In living bone, this 
space is filled with blood vessels and nerves. Food passes through the blood 
vessels to the cells, and wastes from the cells are diffused into the blood 
vessels. The bone cells take calcium salts from the blood and deposit these 
minerals around their irregular projections. 

A. Explain why bone cells with irregular projections of cytoplasm 
deposit greater amounts of intercellular mineral matter than they would 
if these cells were perfectly round. 

B. Suggest a material that probably fills the spaces among the bone 

C. Draw a single bone cell five times larger than it appears under the 

D. Draw a group of bone cells showing how they fit together and 
how they are arranged around the space through which the blood vessels 
run. Label cell, intercellular material, and canal. 

II. Mount a prepared slide of hyaline cartilage under the microscope. 

A. Describe the shape of the cells. 

B. Describe the formation of the cells. 

C. What evidence of intercellular material is there ? The intercellular 
material of hyaline cartilage appears homogeneous throughout. 

D. Draw a group of cartilage cells. Label cell, intercellular material, 
or matrix. 

Cartilage and bone are closely related in their development, 
location, and function. In the embryo, the bones are first pre- 



ceded by qartilage. In infancy, the 
bones of the skull are soft and flex- 
ible, because they are largely carti- 
lage. One can observe the soft 
texture of certain parts of an in- 
fant's skull until the child is about 
eighteen months old. As growth 
takes place, this cartilage becomes 
hard and rigid by the deposit of 
mineral matter. This compact sub- 
stance is then called bone. A child's 
back should be carefully supported be- 
cause its backbone is largely cartilage 
and is, therefore, very elastic, and 
may bend so much that the organs of 



Magnified cross section of bone showing the arrange- 
ment of cells and canals through which blood vessels 
run. The outer covering, periosteum, and the center 
filled with marrow can be seen in the lower diagram. 

Certain cells, cartilage cells, occur 
in pairs. They deposit a thick, tough 
extracellular material called a matrix. 

the body will be injured. 
When a bone is broken, 
the new part first de- 
velops as cartilage and 
is replaced, afterward, by 
true bone. The type of 
cartilage studied in the 
laboratory exercise is 
hyaline cartilage. It is 
found chiefly on the ends 
of bone. This is not the 
only kind of cartilage 
found in the body. 
There are other types 
with different functions. 
One function of cartilage 
is to give ease to the 
motion of joints, and by 
means of its tough elas- 


ticity build those parts of the body, such as the ear and voice box, 
that require strength combined with some elasticity. The inter- 
cellular substance of cartilage is a secretion of the cells. 

flEffiU?*i£5SV Tlie I>roper s rowtn of 

■3P^«3iP^ ji f^S^ bone depends upon suffi- 

^S^N^^M J^$ dent Hine SaltS in the f °° d 

and the presence of certain 

jbone ceU valuable growth promoters 

iDone, . found in food, called vita- 

canal mins, which stimulate the 

proper use of the lime salts 

:gular projections of protcw V the bone Cells « If bone 
plasm deposit calcium compounds which they obtain foes not develop properly, 
from blood. An individual bone cell is also shown. j ■> 

skeletal deformities, like 
bowlegs, may occur. This will later be discussed in connection 
with vitamins. 

Problem. Study of other supporting tissues. 

I. Place a prepared slide of fibrous tissue under the microscope. 

A. Note the large deposits of wavy white fibers with cells scattered 
among them. The white fibers are the intercellular material which was 
secreted by the cells. 

B. Draw a few cells with the surrounding fibers enlarged five times. 
Label the cells and intercellular fibers. 

II. Place a prepared slide of fat or adipose tissue under the microscope. The 
large space filling the center of each cell is a vacuole filled with stored oil. 
The cytoplasm lies just within the wall, crowded there by the enlarged vacu- 
ole. The nucleus can be noticed within the cytoplasm. 

A. Describe the adaptation of adipose cells for fat storage. 

B. Draw a group of adipose cells. Label cell membrane, nucleus, cyto- 
plasm, and vacuole. 

Fibrous, elastic, and adipose tissues. The white fibrous tissue is 
made strong and flexible by the intercellular fibers which are prob- 
ably secreted by the cells. It builds ligaments , strong flexible bands, 



Compare this photomicrograph of a cross section 
of bone with the diagram shown on page 79. 

that hold the bones together at the joints. The tendons are also 

made of it. These attach muscles to the bones and are commonly 

called cords. In bending the 

wrist or stretching the neck, 

these cords are easily seen. 

When elastic fibers predom- 
inate in connective tissue, it 

gives a yellowish color to the 

tissue and is known as elastic 

tissue. It is more elastic than 

fibrous tissue but not so 

strong. It is found between 

adjacent vertebrae, insuring 

elasticity to the vertebral 

column. It is also found in 

the walls of blood vessels. 

The adipose cells store excess supplies of fat. These cells com- 
pose, to a large extent, the yellow marrow of bone. Deposits 

of fatty cells are in the 
deeper layers of the skin 
and encase organs such as 
the kidneys and heart. 
When the fat is needed 
by the body for metabo- 
lism, certain enzymes in 
the cell enter the vacuole 
and digest the fat. 

In general, the cells of 
connective tissue support 
the organs and make the 

Droplets of oil enter certain cells. This oil in- ° 

creases in volume by additional particles entering framework of the body, 
the cells and crowding the protoplasmic contents of 

the cell into a small mass. The cell becomes dis- The tOUghneSS of tendons, 

torted. The oil may be transformed to fat. Masses of . mi p 

these cells build the fat or adipose tissue of the body, the extensile Character 01 




connective tisdtte 



elastic tissue and cartilage, and 
the hardness of bone are all due 
to the composition and distribu- 
tion of the intercellular material 
of the connective tissue cells. 


1. What is meant by secretion? 

A. Name four materials mentioned 
in this chapter secreted by cells. 

B. Give the purpose of each material. 
Name three types of epithelial tissue. Tell the function of each. 
What does the burning of bone show you ? 

What effect do some acids have on a bone ? 

Why should the food of an infant contain mineral matters ? 

Arrange in tabular form the names of the tissue cells discussed, 

Certain connective tissue cells deposit 
long strands of extracellular material in the 
form of either yellow or white fibers. 

the function of each, and an adaptation for each function. 




Babe Ruth, home run king. 

Helen Wills, queen of tennis. 

Why is the body able to move? What tissue in the body makes 
movement 'possible? How are messages carried from one part of the 
body to another? In what way are the different tissues structurally 
related? What brings about coordination among the different parts 
of the body? Why may blood be considered a tissue? 

Muscular tissues. All movement in the human body is brought 
about by muscular or contractile tissues. Whether it is the raising 
of an arm, the swallowing of food, the beating of the heart, con- 
traction of the pupils of the eye in response to light, or the forma- 
tion of so-called goose flesh in the skin when the body is cold, 
the movement is the result of changes in the muscular tissue. 

Problem. Gross structure of skeletal muscle (unmagnified) . 

Secure some fore shank of meat from the butcher. • Be sure to obtain a 
piece that shows the attachment of some of the meat to the bone. Have the 
butcher cut it up into enough sections to supply the class. 

The meaty part of the shank is composed largely of a type of muscle called 
skeletal muscle because it moves the bones of the skeleton. This muscle is also 
called voluntary because it is under the control of the will. 

I. Observe and describe the appearance of the muscle that is attached 
to the bone. The contracting or shortening of this type of muscle will move the 
bone by means of the strong inelastic tendons which are fastened to the bone. 

II. Find a piece of beef showing the outside of the muscle. Describe the 
appearance of the covering or sheath. It is made of connective tissue. 






III. Tear or separate the muscle into parts. Notice that the muscle is 
divided into little bundles. Try to remove one of the little bundles from the 
others. Name and describe the tissue that separates one bundle from another. 

Describe the shape of each little 
bundle. Describe the arrangement 
of the bundles in making up the en- 
tire muscle. 

Problem. The structure of skel- 
etal muscle. 

_ Select a tiny muscle bundle ; place 
it flat on the glass slide and add a 
drop of dilute iodine. Cover with a 
cover glass and focus under low 
power, then high power. 

I. Observe the long individual 
muscle fibers and find the tiny cross 
markings called striations. Skeletal 
muscle is often called striated muscle 
because of the presence of these char- 
acteristic cross markings. 

II. Draw two or three muscle 
fibers five times larger than they 
appear under the microscope. Label 
fiber and striations. 

III. Examine a prepared slide of 
striated muscle. Describe the ap- 
pearance and location of the nuclei 
scattered along each fiber. 


A muscle is made of bundles of muscle 
fibers, each bundle surrounded by connective 
tissue. A thick external layer of this connec- 
tive tissue is continuous with the tendon which 
is composed entirely of connective tissue. 
The tendon joins the muscle to a bone. 

Problem. The structure of smooth or involuntary muscle. 
Mount a prepared slide of smooth muscle under the microscope. 

I. How does smooth muscle differ from striated muscle in appearance and 
shape of fiber and in nuclei ? 

II. Smooth muscle is called smooth or unstriated muscle because of the 
absence of cross-striations. It is also called involuntary because it is not under 
the control of the will. It is found in many internal organs such as the walls 
of the stomach and intestine, and is responsible for movement in these organs. 

III. Draw and label two or three smooth muscle cells. 



Muscle tissue. It is impossible to discuss muscles without 
bringing in a discussion of other tissues. When a large muscle is 
dissected there is found not only the basic muscle cells, but several 
other related tissues. The muscle is completely covered by a 
sheath of connective tissue which extends in through the muscle, 
dividing it into large bundles, then smaller and smaller ones, until 
the bundles, or fasciculi, are so tiny that they are almost micro- 
scopical. This connective tissue furnishes support for the blood 
vessels and nerves which run through the muscles. Deposits of 
fat cells may sometimes be found within the muscular tissue. 

Three kinds of muscles may be identified : cross-striated or skele- 
tal, unstriated or smooth, and a specialized type which forms the 
substances of the heart, called cardiac muscle. The units in stri- 
ated muscle are probably the fibers. They have many nuclei in 
contrast to the single nucleus in the elongated spindle-shaped 
cells of the smooth muscle fibers. Skeletal muscle is voluntary 
muscle. It is under the control of the will. Smooth muscle and 
cardiac muscle are involuntary or independent of the will. Car- 
diac muscle resembles vol- 
untary muscle in having 
cross striations. 

The special function of 
all muscles is the produc- 
tion of motion or the ex- 
ertion of physical force. 
This is brought about by 
the shortening or contrac- 
tion of the muscles which 
have the ability of return- 
ing to normal condition. 
These changes are known 
as contraction and relaxation. Normal muscle cells are always 
in a slight state of contraction known as muscular tone. This 


carcLiac smooth 

There ar» three types of muscle cells. Those having 
many nuclei and cross markings are called striated cells. 
The spindle-shaped ones with a single nucleus aie 
smooth muscle cells. An intermediate form, cross- 
striated with a single nucleus, is found in the cardiac 
muscle cells. Compare the three types. 




Muscles work in pairs. Motion is caused by the pull 
resulting from muscular contraction. If the biceps con- 
tracts, the triceps relaxes; the forearm is thus pulled up. 

keeps the muscles in a condition ready for work. Muscles always 
exert a pull, not a push. Skeletal muscles usually occur in pairs, 
one of which opposes the other. For example, in front of the 

upper arm there is a 
muscle called the flexor 
and on the opposite 
side, the antagonizing 
muscle called the ex- 
tensor. The former 
causes the forearm to 
bend and the latter 
causes it to extend. 

Nerve tissue. The 
organs of the body are 
composed of various tissues. These tissues and organs are inter- 
related and brought into communication by means of the nerve 
tissue. As telephone wires bring various homes of a community 
into communication, so nerve tissue brings the various organs 
into coordination. For example, we see a coin on the floor and 
pick it up. The eyes in seeing, the mind in deciding, the body 
in bending, and the fingers in picking up, all work in proper 
sequence due to regulation by the nerves. The muscles actu- 
ally do the work but the nerves control 
the muscles. Muscles are kept in proper 
tone by repeated stimulation from the nerve 

If a nerve cell is examined microscopi- 
cally, the cell body, cyton, with branching 
projections of protoplasm and with one long 
process is easily seen. The branching pro- 
jections are the dendrites and the one long 

A nerve is a bundle of 

process is the axon. The nucleus lies near axons. Each bundle is sur- 

, . ., ., , , „ - rounded by a fatty protec- 

the center or the cell body. By means of tive sheath. 






the dendrites, nerve cells connect with each other. The axon 
is the process which connects the nerve cell with a structure 
remote from the cell body. 

If one hears a sound and walks toward 
it, an axon has carried the sound from 
the ear to a nerve cell in the brain. By 
means of dendrites, a connection was set 
up with another nerve cell which in turn 
carried the message to muscle cells. The 
muscle cells contracted so as to make 
walking possible. Axons vary in length : 
some are microscopic while others may be 
as long as two or three feet. The cell 
body is always of microscopic dimensions. 
Nerve cells attain the highest development 
of irritability. They are the highly sensi- 
tive cells of the body. They receive mes- 
sages, transmit them, and regulate the 
responses to these messages. Nerve tissue 
will be studied in greater detail in a later 

Blood tissue. Blood is so highly fluid 
that it is not usually considered a tissue. A tissue has been 
defined as a group of similar cells, and blood, consequently, may 
be considered a tissue since it consists of groups of similar cells. 

Problem. Study of blood tissue. 

Press the finger near the tip until blood congests. Prick the end of the finger 
with a needle that has been passed through a flame to sterilize it. Touch a 
cover glass to the drop of blood on the finger ; invert the cover slip on a glass 
slide. Mount under the low, then under the high power of the microscope. 

I. Describe the shape, size, and color of the more numerous cells seen. 
These are the red corpuscles. 

II. Examine all the substance under the microscope carefully and find 
an occasional irregularly shaped cell. This is a white or amoeboid corpuscle. 

terminal branches. 

The unit of nerve structure 
is called a neuron. This cell 
has several processes, one 
sometimes very long, the axon. 
Although the cell body, cyton, 
is microscopic, the axon, also 
microscopic in diameter, may 
be two or three feet long. 



Blood corpuscles. The red corpuscles are circular, biconcave 
disks lacking nuclei. There are* approximately five million in a 
cubic millimeter of normal human blood. They have a yellowish 
red tinge when viewed singly, but in great numbers appear red. 
This color is due to an iron-bearing compound, haemoglobin, 
which is in the cytoplasm. This haemoglobin readily unites 
with oxygen and just as readily gives it up when oxygen is scarce. 
The red corpuscles, in spite of their extremely minute size, can 
carry large quantities of oxygen. Human tissue cells are not in 
direct contact with the oxygen of the air. Therefore, they de- 
pend upon the specialized red corpuscles for their supply of oxygen. 
The white corpuscles are irregular masses of cytoplasm con- 
taining one nucleus or several nuclei. Normally, they number 
between eight thousand and nine thousand to a cubic millimeter. 
They move and feed in a manner similar to that of amoebas. 
They send out projections' of protoplasm which engulf and digest 

foreign materials. They are 
sometimes called the scaven- 
gers of the body because they 
rid the body of germs and 
other foreign material. Un- 
like other body cells, they 
have the power of independent 
motion and can move in a di- 
rection opposite to the blood 
current. They can even make 
their way out of blood vessels 
and get into the surrounding 
tissues to destroy germs. 

Specialization of human 
tissues. It is evident from 
the preceding chapters that the different tissues of the body are 
adapted to perform particular functions. Epithelial tissue is 

Part of a drop of blood that has been magnified 
2500 diameters and then enlarged. The cell 
shown in the center with a large nucleus is a 
polynuclear white corpuscle. 



Compare this magnified drop of frog's blood 
with the human blood. This is not enlarged as 
many diameters as the preceding photograph. 
Notice the oval shape of the red corpuscles and 
the nucleus in each one. 

highly specialized for secretion, absorption, and protection; 
muscle tissue, for contraction; connective tissue, for binding 
together various parts of 
the body and for support; 
nerve tissue, for transmitting 
stimuli ; and blood tissue, for 
circulating materials . In gen- 
eral, the cells of all tissues 
can perform all the cell func- 
tions that are necessary for 
the life of the cell. When 
cells are highly specialized 
and are not in direct con- 
tact with the outside world, 
some of their functions be- 
come reduced and are practi- 
cally lost. Then these cells 
become dependent upon each other to such an extent that life 
is impossible without this interdependence. 

The tissue cells of higher animals do not have to seek food. 
They are supplied with food by the blood. Certain cells store 
small quantities of animal starch or glycogen and oil. These par- 
ticles may be digested by the cells when the need arises. Assimi- 
lation and growth remain as functions of all cells. Cells obtain 
oxygen from the blood, oxidize the food for the release of energy, 
and use this energy for their work. The muscle cells and white 
corpuscles release energy, in the form of mechanical energy, par- 
ticularly for motion. The epithelial cells use chemical energy, and 
nerve cells use nervous energy. The connective tissues and red 
corpuscles need only sufficient energy to perform their general cell 
functions. Most of the tissue cells lose their power to divide mi- 
totically. The epithelial cells and the white corpuscles are the 
only ones, thus far studied, which retain this power throughout life. 

WH. FITZ. AD. BIO. — 7 


Questions and Suggestions 

1. Name all the tissues of the hand and give the function of each. 

2. Compare muscle, nerve, and blood tissues in function and in 
adaptations of their structure for the function mentioned. 

3. Compare a Paramecium and a tissue cell with respect to functions 
and adaptations for function. 

4. Compare a Spirogyra cell and a tissue cell as to functions and 
adaptations for function. 

Supplementary Readings 

Kimber and Gray, Textbook of Anatomy and Physiology (The Macmillan Co.). 
Stohr, Textbook of Histology (P. Blakiston's Son & Co.). 
Williams, Jesse F., Healthful Living (The Macmillan Co.). 


When broken into elements 

man is worth eighty-two cents. 

What is a food? What is the relation of a nutrient to a food? 
What is meant by dietary requirements and dietary deficiencies f 

Since the cell is the basis of our make-up, and since these cells 
live, grow, and work, each must have food and oxygen to carry 
on the various life processes. The cells of the brain must have 
food and fuel to do the part each does in the thinking process. 
Muscle cells in the thumb and fingers must be nourished and given 
oxygen if they are to do their work. 

What is a food ? A beefsteak includes lean meat, fat, and bone. 
Only a part of this can be used by the body. This part is nu- 
tritious. Potatoes contain about 70 per cent of water and vary- 
ing amounts of starch, protein, and mineral salts. As a matter 
of fact, they contain only about 25 per cent of nutritive material. 
The small per cent of cellulose which makes up the cell walls has 
no more real food value than the wood of a lead pencil. It passes 
through the food tube, unaffected chemically. Such parts of the 
potato are called waste. Thus we see that every food may contain 
both nutrients and wastes. Certain of the waste materials that 
pass through the food tract undigested, serve the real and de- 
sirable purpose of giving bulk to the diet. 

What is a nutrient ? Any substance, such as carbohydrate, pro- 
tein, or fat, that yields material for growth and repair of tissues or, 




when oxidized, can be used as fuel for the release of energy, is a 
nutrient. The term nutrient is frequently used to denote the 

Malnutrition exists among plants as well as animals. Many different minerals are essen- 
tial for the best growth and development of plants. When soil is properly fertilized, it con- 
tains all the essential mineral matters. Note the relation of minerals to plant growth. 

whole food, but foods are really made of combinations of nutri- 
ents. The energy which was originally stored in the food by the 
plant during the process of photosynthesis, is released from the 
food during the oxidation process in the body. This stored 
energy is set free from the food in some active form ; such as, 
muscular energy, chemical energy, heat energy, or nervous energy. 
When sugars and fats are burned, either over a fire or in the body, 
waste products, carbon dioxide and water, are formed ; when pro- 
tein is burned in the body, nitrogenous wastes, containing some 
urea and uric acid, are formed in addition to carbon dioxide and 
water. All foods do not yield the same amounts of energy. The 
oxidation of those foods in which sugars and fats are concentrated 
in the greatest amounts, yields the most energy with the least 
amount of waste. The best fuel nutrients are sugars and fats, 
and the growth or building nutrients are proteins, salts, and water. 
When the diet contains an insufficient amount of sugars and 
fats, some of the proteins may be oxidized for the release of energy. 
But proteins give off great amount of wastes which the body 
usually has difficulty in disposing of effectively. 



The energy in food is measured in terms of heat units called 
calories. A calorie represents the amount of heat required to 
raise the temperature of one gram of water one degree centigrade. 
When we deal with food values, we use the large calorie, which 
is 1000 times the small calorie. In other words, the large calorie 
is the amount of heat required to raise one kilogram (1000 grams) 
one degree centigrade. When we speak of the caloric value of a 
food we mean the power of food to yield heat units. Food chem- 
ists group our food nutrients into the five classes which were 
studied in general science or elementary biology. The table on 
page 94 will help you recall certain facts concerning these classes 
of nutrients. 

Complete and insufficient diets. Even if a person ate some 
of- all the nutrients, it would not necessarily mean that he was 
getting a sufficient or a complete diet. If the diet is composed 
entirely of the nutrients from the same food, it is usually insuf- 
ficient, and the person using this diet may suffer from malnutri- 
tion. Careful investigations have disclosed that 15 to 25 per cent of 
the children in the United States are suffering from malnutrition. 

Gliaden and milk diet 

Gliaden diet 

Rats need a variety of food materials. These four-month-old rats are from the same litter 
and have been fed the same quantity of food, but of different variety. Note the differences 
in size. 

Protein insufficiency. An investigation was made, by McCollum 
and others, in a certain institution for children to discover the 






as a 
K o 






Xantho-proteic test ; 
add nitric acid, heat, 
then cool and add am- 
monia — orange-yellow 
is positive reaction. 






. w 








A. Iodine-positive reac- 
tion is blue. 

B. When heated to boil- 
ing with Fehling's solu- 
tion, the positive reaction 
is a brick-red color. 

Burn the substance — 
if an ash is left, mineral 
matter was present. 

Heat the substance — 
if vapor comes off, the 
substance contains water. 
















Builds new tissue and repairs 
cells of the body; can supply 



s . 

. °3 

Furnishes energy for the 
body in the form of heat 
and work. Transformed into 

Helps to build bone, and other 
tissues, and aids coagulation of 
the blood. Essential constitu- 
ent of protoplasm. 

Used as vehicle to carry 
nutrients; is a solvent. It is 
a regulator of the temperature 
of the body and enters into, 
making of all cells. 
















A. White of egg 

B. Rye, wheat 

C. Milk 

D. Wheat 

E. Lean of meat 

F. Corn 

Fat of meat ; but- 
ter, olive oil, oil in 
corn and wheat 

13 • 
C3 © 

8 "8 

2 2 
« © 

















1— 1 





Carbon, hy- 
drogen, nitro- 
gen, sulphur, 
oxygen, phos- 

Carbon, hy- 
drogen, oxy- 

Carbon, hy- 
drogen, oxy- 
gen (hydro- 
gen and oxy- 
gen always in 
the same pro- 
portion as in 
water, H2O) 

Sodium, phos- 
phorus, • sul- 
phur, calcium, 
and others 


a g 









I. Protein 

A. Albumen 

B. Gliaden 

C. Casein 

D. Glutenin 

E. Myosin 

F. Zein 




r 03 

III. Carbohydrates 

A. Starch 

B. Sugar 






















cause of so many cases of malnutrition. The institution was in 
excellent condition as far as ventilation, sanitary facilities, sun 
porches, playgrounds, and careful supervision were concerned, 
but severe malnutrition existed among the children. A careful 
study of the food of the children showed that there were suffi- 
cient nutrients in the foods given in the diet, but that the pro- 
teins were supplied chiefly by lean meat. The children were 
then divided into two groups. In one group, a quart of milk 
was added to the daily diet of each child. In the other group, the 
children continued on the original diet without the milk. Within 
a short time there was a marked increase in body weight among 
the children in the milk-fed group. The increased weight was 
maintained, and there was a noticeable change in behavior. The 
milk-fed group became much more active than the group of 
children not receiving milk. From this and similar experiments 
it was concluded that a diet composed largely of cereals, vegeta- 
bles, meat, and bread does not prove satisfactory for the physical 
development of the young children and that the addition of milk 
furnishes the supplementary food for the type of diet that is lack- 
ing in sufficiently varied animal proteins. It has also been found 
that the proteins in peas, beans, and other vegetables are of less 
anabolic (pertaining to the building of protoplasm) value than 
those in milk, egg, and meat. 

Mineral insufficiency. There seems to be a marked tendency in 
the average American, to-day, to have proportionately too little 
calcium in his diet in relation to the amount of phosphorus. It 
may be partly in consequence of this, that millions of the school 
children of the United States have been found to have defective 
teeth. The calcium must not only be present in the diet, but 
must be in such a form that the body is able to use it. The 
utilization of calcium will be more fully discussed in a later 
chapter. The list on the following page gives some of the com- 
mon foods that contain various minerals. 



Sodium — common salt. 

Potassium — meat and vegetables. 

Magnesium — meat and vegetables. 

Calcium — milk and leafy vegetables. 

Sulphur — meat and vegetables. ' 

Phosphorus — cheese, cod, haddock, celery, spinach, and lettuce. 

Iron — meat, milk, eggs, whole wheat, spinach, and 

Iodine — milk, leafy vegetables, fruits, and water. 

If the diet is widely varied to include a great many different 
foods, sufficient minerals are obtained. When the diet is not prop- 
erly varied, specific minerals are sometimes prescribed by doctors. 
For example, limewater is put in the milk of infants, or medicines 
containing iron are given children. The body utilizes to some 
extent the minerals in this form. However, it is cheaper and 
better to get the minerals from food. Here, they are bound 
chemically with organic substances, in which form they are easily 
assimilated by the body. 

Vitamins. Certain of our foods are of great use to the body in 
that they are health regulating. It is known that such foods 




v eye 




• •*-*»** 

Vitamin C 







in. rat5 

Vitamin. G 

, or- 


contain certain sub- 
stances known as 
vitamins. Little is 
known of the physi- 
cal and chemical 
properties of vita- 
mins, although a 
great deal of re- 
search is being done 
in this field of nu- 
trition. The amount 
of vitamins in food 
has not yet been 
measured in definite units, but is expressed by relative terms such 
as abundant, rich, fair, poor, and deficient. 

Vitamins, a long-known need. Writings of the ancient Greeks 
show that scurvy, now attributed to a diet deficiency, was then 
known, but not understood. The person suffering from this disease 
loses weight, is anaemic, pale/and weak. During the Middle Ages, 
the records of the Crusaders show that this disease occurred fre- 
quently. The Crusaders attributed it to something injurious in 
the diet rather than to the lack of some requirement. Indeed, 
armies of nearly all countries have suffered from scurvy during 
wars. It has appeared whenever extended campaigning or other 
conditions have limited the opportunity to get fresh and varied 

At one time it was impossible to supply sailors on long voyages 
with fresh foods. Captain Cook, the English explorer and trader, 
was one of the first to recognize the value of fresh food as a protec- 
tion against scurvy. His extended voyage, which was begun in 
1772, was much discussed because no scurvy appeared among the 
This was true even though the voyage lasted over three 


years and covered vast stretches of the South Pacific and South 



Atlantic Oceans. Such a conquest of the ancient scourge was un- 
known up to that time. Captain Cook attributed his success to the 
liberal use of such fresh fruits and vegetables as could be obtained, 
and to the frequent use of sauerkraut and barley. Partly on 
account of this experience and partly because of similar observa- 
tions and controlled experiments, regulations for the British navy 
have required, since 1795, that all ships' crews be supplied with 
fruit juices (usually limes) and vegetables which were thought to 
prevent scurvy. (Because English sailors eat limes for the vita- 
min in lime juice they are often called " limeys.") Not only armies 
and navies, but exploring expeditions, camps of lumbermen, and 
other isolated communities of persons have suffered from scurvy. 
Although this disease had indicated, during all centuries of re- 
corded history, that some peculiar food substance was required, 
recognition of the vitamin-character of the substance which 
prevents scurvy came only in recent years (1919-1920). 

A similar story is 
found in the history 
of the peculiar dis- 
ease called beriberi. 
This has also been 
one of the ancient 
scourges of certain 
races. Definite rec- 
ords, dating back to 
an extremely remote 

The diets of these two rats of the same age were alike in 
every respect except in the kind of fat. The rat on the right 
received butter which contains vitamin A; the rat on the left 
received lard which lacks vitamin A. The stunted rat devel- 
oped an eye disease. 


period, appear 
Chinese writings, 
telling of the rav- 
ages of beriberi. 
Beriberi is characterized by inflammatory changes in the nerves 
and it usually involves distortion and even paralysis of the limbs. 
Like scurvy, this disease may prove fatal if it is not counteracted 


by appropriate foods. Beriberi occurs frequently in Asiatic coun- 
tries where rice is the staple article of food. The unquestioned 
prevalence of the disease among rice-eating people led to ^the 
theory that a fungus or 
bacterial growth in rice 
might be the cause of this 
disease. However, a de- 
ficiency in the vitamin diet 
is now generally held to be 

thp pnn«5P nf tli k rh'<?Pn<?P Funk fed P 1 ^ 01155 of ihe same a S e &* same amounts 

uie cdUbe ui uiib ui&ed&e. of rice# The one on the left ate whole rice The one 

PrAc^nt Aav IrnnwrlAHo-A on the right was fed polished rice which lacks vita- 
.rre&eiu uay Kiiuwieuge min B ^ gecond pigeon . g showing sym p toms f 

Of vitamins. The experi- polyneuritis which can be cured by feeding it foods rich 
" in vitamin B. Polyneuritis is also found in people. 

ments performed in the 

last few years have given us considerable knowledge of vita- 
mins. Unless we include them in the diet, deficiency diseases 
may result. 

An interesting experiment was carried on to determine the diet 
essential for the normal development of rats. Baby rats were fed 
equal amounts of food with proper kinds and proportions of pro- 
teins, carbohydrates, and mineral matters, but one group was given 
fat in the form of lard and the other given butter instead of the 
lard. The rats fed on lard failed to grow normally and they soon 
developed sore eyes. The butter-fed rats grew into normal 
healthy rats. Lard lacks the vitamin known as the fat-soluble 
vitamin A. This vitamin occurs in milk, butter, cod-liver oil, egg 
yolk, and in the leafy green parts of vegetables such as spinach, 
lettuce, and cabbage, and in the yellow pigmented parts of plants 
such as carrots and sweet potatoes. The lack of vitamin A causes 
stunted growth, and a certain eye disease, xerophthalmia, which 
may result, in permanent blindness. Taken in its early stages, 
however, this disease can be cured by including in the diet some 
foods containing vitamin A. 

In another experiment, two groups of pigeons were fed, one on 



Two guinea pigs of the same litter were fed 
standard diets. The one on the right did not 
get any vitamin C. It lost weight, and devel- 
oped scurvy which is a type of malnutrition. 

polished rice and the other on whole grains of rice. In a short 
time, the first group developed a peculiar nervous disease, polyneu- 
ritis or animal beriberi. The 
group fed on whole rice re- 
mained healthy. Polished rice 
lacks a vitamin known as vita- 
min B. When the polyneuritic 
sufferers were given food or 
water solutions made from rice 
polishings, they recovered. 
Vitamin B occurs in yeast, milk, and in the hulls or outer cov- 
erings of grains and fruit. In fact, this vitamin is found in so many 
common foods that it is probably only an extreme diet of some 
kind that will induce beriberi. 

Two sets of guinea pigs were fed a diet containing evaporated 
powdered milk in addition to the basal foods required. In the 
case of one set, the 
milk was heated for a 
long period ; the other 
set of pigs was fed the 
unheated milk. The 
first group developed 
scurvy ; the second 
group remained 
healthy. Tests show 
that vitamin C, which 
is present in milk and 
the lack of which 
causes scurvy, is, in a 
large measure, de- 
stroyed by heat. Pas- 
teurization of milk, therefore, may destroy this vitamin. For this 
reason, babies that are fed on pasteurized milk should be given 

Leg disease, a type of rickets, may be due to lack of vita- 
min D. These chickens are the same age and received the 
same amounts of different foods. Food containing vitamin 
D or even sunlight will help to prevent and cure rickets. 






' D 

, £,. 



Lean muscle 


























Pork, lean 













•• fat 



Potatoes, white 








Beans, kidney 






Beans, navy 






































Peas, fresh 













Fish, roe 

























Brazil nuts 







Mushrooms w 














Hickory nuts 





Cod Liver Oil 










Corn Oil 


Walnuts, English 


Margarine, oleo 


■• black 


Mutton fat 



Beef fat 



Milk, whole 
" skim 









"• condensed 





«■ •• sweetened 







«• evaporated 








" powdered 

















Cheese, whole milk 



Lemon juice 












Limes . 




Molasses, beet 


Orange juice 





•« sorghum 


Tomatoes, raw 





•• cane 


•• canned 













Eggs, yolk 









. ■•-:- 




Wheat, whole 







Jt * 



" germ 




Green grass 




" bran 







Corn, white 






<> yellow 




Rice, bran 














other foods to supply this vitamin. Vitamin G occurs largely in 
citrus fruits such as lemons and oranges, and in tomatoes and 

Underwood & Underwood 
Sunbaths are valuable for insuring the proper functioning of the body. Irra- 
diation guarantees an optimum storage of calcium in the body. 

cabbage. During the early days of the great World War, before 
the United States had entered the fight, a foreign ship entered 
Hampton Roads with hardly enough healthy sailors to man the 
vessel. The ship had been transformed into a commerce raider, a 
gun had been mounted both forward and aft, and the hold was filled 
with enough canned and concentrated foods to provision the crew 
of sailors and marines for many months. But fresh foods were 
lacking and the crew was repeating the experience of many sailors ; 
it was suffering from scurvy. Orange juice, tomato juice, milk, 
raw cabbage, celery, carrots, and water cress, which are known to 
contain vitamin C, were, at once, included in the diet of the sailors 
and they soon recovered. 

Many animals suffer from a disease known as rickets, which is 
an improper formation of bones. This seems to be caused by the 



non-deposit of the mineral calcium which is present in certain 
foods. The head of a rachitic animal usually becomes bulky, and 
the bones at the knees and ankles, become enlarged. For experi- 
mentation, a set of rats was fed a diet which contained vitamin A, 
but lacked another substance known as vitamin D; another set 
of rats was given vitamin D in the form of cod-liver oil. The first 
group developedrickets ; the second group grew normally. : Many 
physicians and scientists have observed and reported that the 
exposure of rachitic children to the rays of the sun has brought 
about an improvement and cure of rickets. In these cases there 
were plenty of calcium and phosphorus already present in the 
blood, and the sunlight is thought to have influenced, in some 
way, the activities of certain cells so 
that they could make efficient use of 
these minerals. Other scientists have, 
found that it is the ultra-violet rays in 
sunlight, which are instrumental in 
preventing and curing rickets. These 
curative rays cannot pass through 
ordinary window glass, but will pass 
through quartz glass. 

If babies are given food deficient in 
vitamin D, but which has been exposed 
to these light rays, the food can be 
activated so as to cause it to have the 
same effects as the ultra-violet rays. 
Cotton-seed oil, which ordinarily con- 
tains no vitamin D, becomes anti- 
rachitic when exposed to sunlight. 

Two scientists, Evans and Bishop, 
have added another member to the 
vitamin family. They found that this vitamin, which they named 
vitamin E, has a marked influence upon the fertility of rats. 

Sunsuits give children the benefit of 
the direct rays of the sun. 


When a diet lacking certain food stuffs which contain vitamin E is 
fed to rats, the reproductive organs of both the male and female 
will be affected. Investigators have found that a deficiency of this 
vitamin in the mother rat will lead to the resorption of the embryos 
even after development has proceeded in a normal manner for a 
week or more. Other research workers have found that this vita- 
min is present in meat, wheat germ, rolled oats, yolk of egg, 
milk fat, and lettuce. 

In the biology of to-morrow, there will probably be other vita- 
mins to add to the group already listed. There has been some 
work with what has been called vitamin G or vitamin P-P (pellagra- 
preventive). Lack of it is known to induce pellagra, a disease 
afflicting many people in the southern states. The late Dr. Joseph 
Goldberger, of the United States Public Health Service, found 
that certain foods contain this pellagra-preventive, but as yet the 
amount of the preventive substance in various foods has not been 
conclusively determined. 

Diets. Malnutrition was at one time attributed to poverty, 
but scientists have found that there is almost as much malnu- 
trition among the wealthy as the poor. Proper dieting is a matter 
of selecting different foods that give all the elements essential to the 
health of the individual. Many dietary studies have been made in 
various countries and among people doing different types of work. 
From these studies and from experiments, certain foods have been 
recommended that are thought to make for physical fitness. 

All diets should include proteins, fats, and carbohydrates, prob- 
ably in the proportions of one, three, and six. They should in- 
clude, among other foods, a quart of milk and some leafy or raw 
vegetable so that a sufficient supply of vitamins can be guaranteed . 

It should be kept in mind that people of different ages, sizes, 
weights, and occupations naturally require different amounts of 
calories of foods. The following table is suggested for determining 
the number of calories of food needed by boys and girls : 




*From 12-13 2300-2700 

From 13-14 2500-2900 

From 14-15 2600-3100 

From 15-16 2700-3300 

From 16-17 2700-3400 

, Girls 

Problem. Study of personal diets. 

I. Consult the age and weight tables in the Appendix and find out whether 
you are normal, underweight, or overweight. 

II. From the table given above, determine the number of calories you need 
per day. 

III. Make out the following outline and list the foods eaten by you on a 
definite day. 




Between meals 

* New York Association for Improvement of the Condition of the Poor. 

WH. FITZ. AD. BIO. — 8 


A. Consult the tables of caloric values of foods in the index. 

1. Fill in the number of calories of protein, fat, and carbohydrates for 
each food you have listed. Total the columns. 

2. Add the totals. Compare your actual totals with the number of 
calories you really need according to the given table. 

a. Are you eating enough, too little, or too much food ? 

b. Is the ratio of protein, fat, and carbohydrates correct ? 

c. Consult the suggestions given in the discussion of foods and see 
-whether all the types of food needed are in your diet. 

3. What changes, if any, should be made in your diet ? 

a. Give reasons in each case. The age-weight tables are not 
authentic opinions as to malnutrition. They are, however, some- 
what indicative of the condition of nutrition. 


1. Define a food and a nutrient. 

2. What elements in foods are fuel for oxidation ? 

3. What are vitamins ? What are their value in the diet? 

4. What are deficiency diseases ? Name several. 

Supplementary Reading 

Harrow, Benjamin, Vitamins (E. P. Dutton & Co. Inc.). 

McCollum & Simmonds, The Newer Knowledge of Nutrition (The Macmillan 

Sherman, Chemistry of Food and Nutrition (The Macmillan Co.). 
Stieglitz, J. O., and others, Chemistry in Medicine (Chemical Foundation Inc.). 



Continuous growth of teeth. 

Fangs of snake inject venom. 

What are some causes of bad teeth? What is meant by the hygiene 
of the teeth f Why are the teeth of the average American probably 
inferior to those of his great-grandparent f 

Detailed structure of teeth. Not only are teeth important in 
helping to prepare food for use in the body, but they are invaluable 
in maintaining the health of the body. The teeth, embedded in 
sockets in the upper and lower jawbones, are especially fitted for 
the work that they have to do. Each tooth has a root which con- 
sists of one or more divisions contained in the socket; a crown 
which projects above the gums ; and a neck which is the narrow 
portion at the edge of the gum. 

Each tooth is composed principally of dentine. In the center 
of the dentine is the pulp cavity which tapers into the root canal 
and ends in a small opening at the extremity of the root. The 
pulp cavity is filled with loose connective tissue containing blood 
vessels and nerves which enter through the root canal. The 
dentine is crowned with a hard layer of enamel composed mostly 
of calcium. The dentine of the root is covered with cement which 
has practically the same composition and structure as bone, but 
is much harder. Every normal person has two sets of teeth dur- 
ing his life, the first or temporary, and the permanent. There are 
twenty temporary teeth, ten in each jaw : four sharp-edged in- 





Todt occrcH 

Blood vessels and nerves 
enter the tooth cavity, which 
consists of connective tissue, 
through the root canal. This 
cavity is well protected by the 
enamel, dentine, and cement. 

cisors, two sharp canines, and four molars especially adapted for 
crushing and grinding. The first teeth of the temporary set usu- 
ally begin to appear when the child is six 
months old and the last appear when he is 
about two years old. The teeth of the 
lower jaw usually develop before the cor- 
responding ones of the upper jaw. 

The permanent teeth push out the tem- 
porary teeth. The milk molars are fol- 
lowed by the permanent premolars, but 
there are no predecessors for the perma- 
nent molars. 
The first permanent teeth usually appear 
about the sixth year while the last ones may not appear until the 
twenty-fifth year. The molars are the first to appear, then the 
two central incisors about the seventh year, the two lateral in- 
cisors at eight, the bicuspids at nine and ten, the canine at eleven 
or twelve, the second molars at twelve or thirteen, and last are 
the third molars or wisdom teeth. 

The first permanent teeth to appear are the upper first molars 
which do not replace any of the milk teeth, but come down behind 
the second temporary molars. When the temporary teeth of chil- 
dren are neglected these six-year molars are often neglected, and 
consequently have to be extracted early in life. 

Arrangement of teeth. When the mouth is closed the upper 
front teeth protrude slightly over the lower front teeth. If the 
teeth are irregular or out of position, this arrangement is changed. 
Adenoids are sometimes responsible for narrowing the jaw and 
throwing the teeth out of position. People with poor formations 
of teeth can not chew their food properly and digestion is therefore 
impaired. When teeth are crowded and out of place, the food may 
remain lodged between the teeth and cause them to decay. The 
normal contours of the face are changed by malformations of the 



teeth. In order to insure good health, teeth should be straightened 
and adjusted. Dentists are usually able to obtain better results 
in correcting these malformations if the teeth are not fully grown. 
Care of the teeth. When the teeth are not cleaned frequently, 
a substance known as tartar often forms upon them, usually near 
the gums, and pre- 
vents the bacteria 

•temporary Canine 
"temporary ny 

twnpownrj£ inoisors ; replaced 'by incisors 


The teeth of a six-year-old child are temporary teeth with the 
exception of the six-year molar. This is the first permanent 
tooth to cut through the gum. Its position is just back of the 
milk molars. 


from being rubbed 
off by the action of 
the tongue. For this 
reason artificial 
means must be em- 
ployed to keep the 
teeth free from this 
gummy tartar 
which later becomes 
hard. The teeth 
should be brushed 
at least twice a day 
with a tooth paste 
or powder which 
contains some sub- 
stance, such as 
chalk, which is hard 
enough to rub off 
all deposits but not 
hard enough to in- 
jure the enamel of 
the teeth. The 
teeth should be brushed with a fairly stiff brush after each meal, 
in order to remove all particles of foods, and to stimulate the 
circulation of blood in the gums. The mouth cavity should then 
be thoroughly rinsed out with a mouth wash or a solution made 

Permanent teeth are for biting, chewing, and grinding. 



by dissolving a half teaspoonful of salt in a glass of warm water. 
Fruit acids such as dilute lemon juice or vinegar should be used 
occasionally. If food lodges between teeth, it should be removed 
by dental floss. A metallic toothpick or pin should never be used 
as it may chip or crack the enamel. Wooden toothpicks should 
also be avoided as they tend to cut and irritate the gums. Silk 
thread is not an adequate substitute for dental floss because it is 
not sterile and it may cut the gums. 

Periodical visits to the dentist. In spite of the best care, the 
tartar cannot be entirely removed from the teeth with a brush. 
The bacteria which are held in the soft tartar will probably 
decay the food left in the teeth. Sometimes the fermenting of 
sugar between the teeth and the acids formed by bacteria will 
dissolve the enamel, causing soft spots or tiny cavities in the teeth. 
The soft dentine is then exposed to the decay action of the bac- 
teria. Once a year, at least, a visit should be made to the dentist 
for the purpose of having the teeth cleaned and any small cavi- 

By skillful dental attention, projecting incisors of the upper jaw can be made to 
articulate, that is, meet the lower jaw. 

ties detected and filled before they seriously weaken the teeth. 
When accumulated tartar remains on the teeth, the gums may 



The contours of a profile may be changed by 
straightening the teeth.. These outlines are 
the profile of a boy before and after he had 
received dental treatment. 

recede, become swollen and inflamed, and the teeth may loosen 
in their sockets. This is one type of pyorrhea which a dentist 
may be able to prevent. 

When the teeth decay, pus is 
frequently formed and absorbed 
by the blood. The pus may 
travel through the body and 
may settle in the valves of the 
heart, causing a heart defect, or 
in the joints, causing rheuma- 
tism. Besides this, decayed 
teeth give the breath an objec- 
tionable odor and the mouth an 
unsightly appearance. Physicians often insist that patients have 
the teeth examined and treated before they will treat them for 
other ailments. The disorder sometimes disappears when the 
teeth are put in good condition. Defective teeth do not have as 
great grinding power as have sound teeth, and, therefore, hinder 

Relation of diets to teeth. More important than repairing 
unsound teeth is the building of sound teeth. Foods containing 
calcium should be eaten so that the bone cells can deposit suffi- 
cient calcium to build strong teeth. Every diet should include 
some foods containing vitamin D, so that the body will be stimu- 
lated to make the greatest possible use of the calcium. Foods 
that demand chewing, such as breads made of whole cereals, toast, 
apples, and celery, are also essential for the development of good 
teeth. Hard foods cause the teeth to move slightly in their 
sockets. This has a massaging effect upon the gums and tends to 
promote circulation through the pulp cavity and the part of the 
gum holding the teeth in the bony sockets. One of the reasons 
why former generations had better teeth than many of the people 
to-day, is because they ate coarser foods which supplied minerals 


and vitamins in greater quantity than our present refined and rich 
foods. The coarse foods act like tiny toothbrushes in scratching 
food particles off the teeth and polishing their surfaces. 

Causes of teeth decay. Other conditions besides lack of indi- 
vidual care may cause defective teeth. A low resistance of the 
teeth to decay is frequently caused by some defect in the devel- 
opment of the individual. For example, some babies have a thin, 
faulty skeletal development which naturally affects the forming 
of the teeth. This may be caused by a deficient diet — both of 
the expectant mother and later of the child. The calcification of 
the temporary teeth and the permanent molars takes place dur- 
ing the child's prenatal life and if the mother does not get the kind 
of food that is essential for the development of the teeth of the 
unborn child, the chances are that its teeth will be defective. 
Again, if a child's diet lacks vitamin D, it is possible that the 
proper amount of calcium for forming teeth will hot be deposited. 
Dental attention to the first teeth is often neglected because 
parents fail to realize the necessity of it or cannot afford the high 
cost of such care. Frequently, the failure on the part of children 
to tell their parents of cavities in their teeth, either because they 
are too young or because they are afraid of being hurt by the 
dentist, is the cause of poor teeth. The lack of competent dental 
facilities in many communities is by no means an infrequent 
reason for bad teeth. 

Problem. Survey of the condition of the teeth. 

Use a mirror or mirrors to assist you in your survey. 

I. Note your bite by closing the teeth and drawing back the lips. 

A. Describe any malformations such as teeth out of place, upper teeth 
protruding over lower teeth, or lower teeth extending over upper teeth. 

B. Discuss the importance of having the teeth straightened. 

C. What is the advantage of having an orthodontist (a dentist special- 
izing in treating irregularities of the teeth) straighten your teeth rather 
than a regular family dentist ? 


II. By means of a small mirror, observe the front surfaces of your upper 
teeth, the inner surfaces of the lower front teeth, and the inner surfaces of the 
back teeth. Use the tongue to explore the surfaces of the teeth for tartar. 

A. Describe the appearance and location of any tartar. 

B. Discuss the origin of tartar. 

III. Look carefully at the gum line of the teeth. Describe the appearance 
of any tooth from which the gum has receded, exposing the neck. 

A. Why will such teeth decay quickly ? 

B. What effect will the removal of tartar and proper massaging of 
the gums probably have on such teeth ? 

IV. By comparing your teeth with the diagram on page 109, name and 
describe the condition of any tooth showing a cavity. In each case describe 
the apparent extent of the cavity. Explain why your examination is not as 
complete as a dentist's ? 

V. If you have any roots of broken teeth left in your gums, give, briefly, the 
history of each. By referring to the diagram determine the name of each. 

A. Discuss whether the loss of the tooth could have been prevented. 

B. Discuss dangers from the presence of roots decay in the mouth. 

VI. If you have any spaces left by extracted teeth, what are your plans in 
regard to these spaces ? Again refer to the diagram to name the missing tooth. 

VII. When did you last visit a dentist ? When will you again visit one ? 

VIII. If you are unable to detect any defects in your teeth, tell why you 
cannot conclude that your teeth are in good condition ? 

IX. By means of red and blue litmus, test whether the reaction of your 
mouth is acid or alkaline. Note. When blue litmus turns pink, an acid is 
present. When pink litmus turns blue, an alkali is present. 

A. State one possible source of acid-formation. What effect has acids 
on enamel ? 

X. What advice can you give your parents in regard to the care of the 
teeth of your small brothers and sisters ? 

XI. Discuss the value of X-rays in dentistry. 


1 . Describe the arrangement, number, and kinds of temporary teeth. 

2. Describe the arrangement, number, kinds, and structure of per- 
manent teeth. 

3. Explain the hygienic methods of cleaning teeth. 

4. What is the relation of proper diets to good teeth ? 

5. What are some of the causes of bad teeth ? 






.dooccal opening 

Part of food tube of worm. 

Alimentary canal of a bird. 

What similarities and differences are found in the digestive sys- 
tems of a frog and of a man. How is food prepared for digestion? 

We shall find in dissecting a frog and studying its digestive or- 
gans that its digestive processes are in many ways similar to those 
of man. 

Problem. Study of the internal organs of a frog. 

Place the frog to be studied in a covered jar. Pour a little ether into the 
jar or put in the jar a sponge saturated with ether. When the animal is 
dead, remove and place it, with the ventral side up and the head away from 
you, in shallow water in an individual dissection pan. • Pin the legs out so 
that they will not interfere with the dissection. By means of forceps, lift up 
the skin in the center of the body and cut a very small opening near the pos- 
terior end. Insert the point of the scissors into the opening and carefully cut 
along a median line to the mouth. Again insert the scissors near the legs and 
cut through the muscles under the skin. Be sure to cut through the pectoral 
girdle of bones near the forelegs. Insert the scissors at the anterior and pos- 
terior ends of the median slit and cut at right angles on either side. Turn 
back and cut off the loosened flaps of skin and the underlying muscles, in order 
to expose the internal organs. If the specimen is a female, remove nearly all 
the eggs so that the organs may be more readily seen. 

I. Make an outline drawing, natural size, of the shape of the frog. 

II. Observe the cone-shaped heart midway between the fore limbs. If the 
heart is still beating, it does not indicate that the animal is alive. It means 



that all of the cells of the body are not yet dead, especially the cardiac muscle 
cells. Draw in the outline, the heart in its proper position. 

III. The lungs lie on either side of the heart partly covered by the liver. 
By means of a blowpipe passing from the mouth to the windpipe of the frog, 
gently innate the lungs. 

A. Account for the color of the lungs. Press them with the wooden 
end of the dissecting needle. Are they spongy or compact ? 

B. What is the relation of the texture of the lungs to the amount 
of air present ? 

C. By means of a hand lens determine and describe the external and 
internal structure of the lungs. Draw the lungs in position in your 

IV. The large, lobed, reddish-brown organ that lies to the right and be- 
hind the heart, and covers part of the lungs, is the liver. It is one of the diges- 
tive glands. Note the greenish bile sac (or gall bladder) attached to the liver. 
Sketch in your outline the liver and gall bladder. 

V. On the left side of the body note the long, tubular, pouchlike stomach. 
Push the handle of the dissecting needle down the gullet into the stomach. 
Draw as much of the stomach as can be seen. 

VI. The tubular structure leading from the stomach and filling the lower 
part of the body cavity forms the intestines. At the lower end of the small 
intestine the tube becomes larger and disappears between the two thighs. 
This large tube is the large intestine, the last part of which is the cloaca. The 
large intestine is similar to the large intestine in higher animals in that it 
excretes the solid wastes of the body, but it is also a reservoir for nitrogenous 
wastes and reproductive cells. In this respect it is different from a true large 
intestine and consequently is called a cloaca. Draw the small intestine, lsfrge 
intestine, and cloaca. 

VII. In the U-shaped loop made by the stomach and the small intestine 
is a small, light-colored, pear-shaped organ. This is an important digestive 
gland called the pancreas. Draw the pancreas. 

VIII. Describe how the internal organs of the frog are held in place. This 
structure is termed the mesentery. 

IX. Label heart, lungs, liver, gall bladder, stomach, small intestine, large 
intestine, cloaca, and pancreas. 

X. After all the required drawings are made, take your specimen from the 
dissection pan and wrap it in mimeograph paper which has been moistened 


in a salt solution. Keep it in a cold place so that you may continue your 
investigation the next day. 

XI. Write a paragraph describing the internal organs of the frog, as seen 
from the ventral view. 

Problem. Study of the food tube or alimentary canal of the 

By means of your forceps, lift up the heart and carefully cut it out of the 
body. Lift up each lung, and carefully cut it out. In a similar manner re- 
move the liver. 

I. Describe the organ leading into the stomach. This is the gullet or 
esophagus. Place the blunt end of the dissecting needle in the anterior 
end of the gullet. Carefully force it through the gullet. Where does it 
lead ? Is the passageway a continuous one or did the needle meet any ob- 
structions ? 

II. Make another outline drawing of the frog and sketch in it the alimentary 
canal. Label gullet, stomach, small intestine, large intestine, and cloaca. 

III. Remove the alimentary canal. The two small brownish red struc- 
tures near the backbone in the center of the body cavity are the kidneys. The 
kidneys remove the nitrogenous wastes (urea) from the blood. Each one is 
connected to the cloaca by a small duct. 

IV. Write a paragraph describing the alimentary canal. 

Problem. Study of the internal organs of man. 
Remove the front wall from the mannikin. 

I. Contrast the chest and abdominal cavities of man with the body cavity 
of the frog. Note the presence of a partition, the diaphragm. 

II. Locate and describe the organs in the chest or thoracic cavity. 

III. Name all the abdominal organs observed in the frog, which can be 
identified in man. 

IV. State four easily recognized differences in structure or position be- 
tween the organs of the frog and man. The large intestine takes care of solid 
wastes only ; therefore, it is a true large intestine and not a cloaca. 

V. Make an outline drawing of the mannikin and sketch the organs in posi- 
tion. Label chest cavity, diaphragm, abdominal cavity, heart, lungs, liver, 
stomach, small intestine, and large intestine. 




Problem. Study of the digestive system of man. 
Remove the heart and lungs from the mannikin. 

I. Locate the gullet and describe its exact position, including origin and end. 

II. Remove the intestines and locate the pancreas and the posterior end 
of the large intestine called the rectum. 

III. Describe the connection of the pancreas and liver with the small in- 

IV. Compare the alimentary canal of the frog and man as to relative size 
of organs and as to complexity in structure. 

V. Make a diagram of the digestive system and label throat, gullet, 
stomach, small intestine, large intestine, rectum, pancreas, and liver. 

The meaning of digestion. Before a cell in the brain, in the 
tip of the toe, or any other part of the body can use the meat 
or the vegetable 
that is eaten, 
many changes, 
physical and 
chemical, must 
take place in the 
food. The organs 
that are particu- 
larly adapted for 
carrying the food 
particles, for pre- 
paring it for ab- 
sorption, and 
making it ready 
for use by the 
various body 
cells, make up 
the digestive sys- 
tem. In the thrashing of grain, much of the useless is sepa- 
rated from the useful parts of the cereal. So, in the digestive 

The digestive organs of the frog have been removed from the 
body to show some of the digestive glands and the continuous ali- 
mentary canal. The bladder is one of the excretory organs which 
drains into the cloaca. The latter is the receptacle for materials 
from the alimentary canal, reproductive organs, and the bladder. 



system, the part of the food that cannot be used is separated 
from the nutrients. This process may be called a refining pro- 
cess. The waste or indigestible 
part of the food is ultimately 
expelled from the body. The 
nutrients are made ready for 
absorption by the action of 
various juices. In this diges- 
tive process the nutrients are 
reduced to simpler and simpler 
organization or certain standard 
forms to enable them to pass 
through the walls of the blood 
vessels. For example, the pro- 
teins in eggs, milk, and meat 
are reduced to standard protein 
products ; the starch in bread 
and potatoes and the sugar in 
fruits, candies, and carrots are 
all reduced to a standard car- 
bohydrate product. The pro- 
cess of digestion really consists 
Man is a collection of tubes and cavities, of refining, digesting, and stand- 

The spinal column is a bony tube, the nerve . 

cord a solid rod made of delicate tissue, and the ardizing processes. 

food tube a long, continuous, pipelike canal. . 

Digestive organs. I he diges- 
tive system may be said to consist of two groups of digestive 
organs, those making up the alimentary canal or food tube in 
which foods are actually digested, and the accessory organs, the 
glands, which make or secrete the juices for digestion. A gland is 
a collection of epithelial cells that secretes a juice. Some of the 
digestive glands are large organs outside the food tube, such as 
the pancreas and liver, and others are minute structures, in the 
lining of the food tube, as the gastric, peptw, and intestinal glands. 

nasal cavity... 
mowfh Cavity- 

fhomcic Cavity 

dxapKrag , iT>- 





gx\\ Naaa<p£ 


When the digestive glands are located some distance from the 
food tube, they have a tube or duct which effects the discharge 
of the secretion into the alimentary canal. 

Alimentary canal of man. The alimentary canal is a tube pass- 
ing through the body, in which food is made ready for the use 
of the organism. While food remains in the canal, it is actually 
separated from the body because it can pass out of the body at 
the posterior end of the tube without having affected the other 
organs of the 
body. Consider 
the alimentary 
canal of the 
worm. It is a , 
straight tube * ive f 
passing from the 
anterior to the 
posterior end of. 
the animal's 
body. It is a 
tube within a 
tube. Before 
food is actually 
in the body, it 
must get from 
that inner tube 
into the sur- 
rounding struc- 
tures. The ali- 
mentary canal of 
man is a contin- 
uous tube from 
the mouth to the anus or end of the large intestine. There is much 
variation in width in various sections, and it is twisted and coiled 







colo TV 

The digestive organs of man are displaced to some extent in this 
illustration, in order to show clearly their relations to each other. They 
are somewhat similar to those of the frog. Note the absence of a 
cloaca, however. Higher animals have a large intestine but no cloaca. 



to a great extent in some parts, but is just as truly a tube as 
the simple straight alimentary canal in the worm's body. The 
alimentary canal consists of the mouth cavity with its accessory 
organs : the teeth, tongue, glands, throat or pharynx, esophagus, 
stomach, the small intestine, and large intestine. 

Mouth. The mouth cavity, nearly oval in shape, is lined with a 
soft membrane which is kept moist by saliva secreted from glands. 
The palate or roof of the mouth consists of a hard portion in front, 
Wkm* ...;£ formed by a bone covered by 

mucous membrane, and of a soft 
portion farther back containing 
no bone. The hard palate forms 
the partition between the mouth 
and nose ; the soft palate arches 
backward, and from the middle of 
its lower border there hangs a 
pointed portion of the soft palate 
called the uvula (little grape). 

The tongue is a muscular organ, 
and has on its upper surface many 
small projections called papillae. 
These papillae contain certain nerve cells that make it possible 
for us to taste sweet, bitter, sour, and salt. When these special- 
ized structures (taste-buds) are stimulated by the food, the secre- 
tion of saliva is increased and gastric fluid in the stomach starts 
to flow. The tongue helps mastication by pushing and rubbing 
portions of the food against the roof of the mouth, and also guides 
the food into position for chewing. The tongue assists in swallow- 
ing by manipulating the food into small masses and pushing them 
back to the throat cavity. 

Due to the complex movement of the lower jaw, up and down, 
forward and back, and from side to side, the teeth shave, slice, 
crush, and grind the food. The broad surfaces of the molars 



There are three pairs of salivary glands 
which empty into the mouth. The teeth 
may become coated with tartar which is par- 
tially a deposit from the saliva. 


help in the grinding process. During this process the food is 
thoroughly mixed with secretions from the glands of the 

The chief secretion of the mouth is supplied by the salivary 
glands. These are three pairs of compound saclike glands, the 
parotid, sublingual, and submaxillary. A parotid gland is placed 
just under and in front of each ear; the ducts from the glands 
pass forward along the cheek and open opposite the second molar. 
The submaxillary glands are situated below the jaw and under the 
tongue, and open into the mouth cavity underneath the tongue. 
Several of the small ducts from the sublingual glands also open in 
the floor of the mouth beneath the tongue. The secretion of these 
salivary glands, mixed with the secretion of the small glands of 
the mucus epithelium, is called saliva. 

Everyone has probably experienced an unusually large flow of 
secretion from the salivary glands when appetizing food is seen or 
smelled. The stimulation of the salivary glands may also be 
brought about by the thought of food that is liked, especially 
when one is hungry. This is known as psychical or mental stimu- 
lation. Flavoring substances and extractives that stimulate the 
taste buds furnish chemical stimuli, and the pressure of food in 
the mouth and the action of irritating substances cause a mechan- 
ical stimulation. 

Saliva. Saliva consists of water, inorganic salts, some mucin, 
and the enzyme ptyalin or salivary diastase. Saliva is usually 
slightly alkaline in its reaction and has four distinct functions : 
(1) it assists in mastication and swallowing by moistening and 
softening the food; (2) it lubricates the food and enables it to 
slide smoothly down the esophagus ; (3) it dissolves dry and solid 
food such as salt and sugar, thus enabling us to taste them, 
and thereby stimulating a further flow of salivary and gastric 
juices; (4) the enzyme ptyalin acts upon starch, converting 
it into sugars, dextrin and maltose. These are intermediate 

WH. FITZ. AD. BIO. — 9 


products in the digestion of starch. They are simpler products 
than starch, but not simple enough to be used by the body. The 
change, due to ptyalin, takes place when there is a slightly alka- 
line condition. Saliva that is distinctly acidulous hinders or arrests 
the digestive process. Boiled starch is changed more rapidly and 
completely than raw, but food is rarely retained in the mouth 
long enough for the saliva to more than> begin the transformation 
of starch. 

Throat and esophagus. The mouth cavity narrows to form 
the pharynx or throat cavity. It is shaped somewhat like a funnel, 
with its narrow or constricted end turned downward to form the 
beginnings of the esophagus and the windpipe. There are seven 
openings in the throat cavity, leading to the nose, ears, mouth, 
larynx, and gullet. Two, in front above, lead into the back of the 
nose and are known as the internal nasal openings. Two, one on 
either side above, lead into the ears and form the openings to the 
Eustachian tubes. One midway in front connects with the mouth. 
Two below, one opening into the windpipe through the glottis and 
the other behind the glottis into the gullet. 

The pharynx is a passageway for air from the nose to the glottis, 
and for food from the mouth to the gullet. When the food is ready 
to be swallowed, it is brought together on the upper surface of the 
tongue and pressed backward into the pharynx. Then the muscles 
in the pharynx contract, drawing the pharynx upward and caus- 
ing it to dilate to receive the food. The muscles then relax, caus- 
ing the pharynx to sink and forcing the food into the esophagus. 
At this instant, breathing is temporarily suspended and the air 
passages closed against the possible entrance of food. The soft 
palate is drawn back, thus closing and protecting the nasal pas- 
sages. The entrance to the windpipe is shielded by being pulled 
forward under the base of the tongue. There is an additional 
safeguard through the folding down of the epiglottis, a special- 
ized cover. When food is once within the esophagus, breathing 


may be resumed. Practically no digestion takes place in the 
pharynx due to the facts that food is swallowed quickly and no 
enzymes are secreted here. 

The esophagus is a comparatively straight tube, about nine 
or ten inches long. It descends in front of the spine, passing 
through the diaphragm and terminating in the stomach. It has 
one set of muscles extending around it circularly and another layer 
of muscles longitudinally arranged. By a series of contractions of 
the circular and the longitudinal muscles, food is passed by a series 
of wavelike movements into the stomach. Once the top ring of 
muscles is stimulated by the swallowing of the food, a wave of 
contraction goes through the full length of the gullet, causing 
the food to enter the stomach. This series of rhythmic, wave- 
like contractions of circular and longitudinal muscle fibers which 
affect successive portions of the tube downward is called peri- 
stalsis. The constricted portion is always preceded by an area 
of relaxation which renders the contraction more effective in 
forcing the contents onward. The direction is normally the 
same, and the action is under the control of the nervous system. 
This movement might be compared with placing a large marble 
in a narrow rubber tube and forcing it through by successively 
pinching the tube. 

During the processes of mastication, moistening, and swallow- 
ing, the food is reduced to a soft, pulpy condition. Any starch 
it may contain begins to change into sugar in the mouth, but 
it remains in the mouth, throat, and esophagus so short a time 
that digestion cannot be completed in them. 

Questions and Suggestions 

1. How does the body cavity of the frog differ from the cavities 
in man's body ? 

2. Name three purposes of the digestive process. 

3. Compare the alimentary canals of the worm, frog, and man, 
stating all similarities and differences. 


4. If saliva were acid in reaction instead of alkaline, what effect 
would it have on the teeth ? 

5. What are the functions of the soft and hard palates ? 

6. State the uses of the tongue. 

7. What is the importance of saliva in digestion ? 

8. Describe the protection of the various openings from the throat 
during the action of swallowing. 

9. Define peristalsis. Discuss the importance of peristalsis in the 
digestive process. 

Supplementary Readings 

Howell, Wm. H., Textbook of Physiology (W. B. Saunders Co.). 

Kimber, D. C, and Gray, C. E., Textbook of Anatomy and Physiology (The 

Macmillan Co.). 
Martin and Weymouth, Elements of Physiology (Lea & Febiger). 





Large globules of fat. 

Separated in an emulsion. 

What changes does the food undergo in the stomach and intestines ? 
What is the importance of gastric juice in digestion? How is the 
small intestine adapted for carrying on digestive activities? What is 
the importance of absorption? 

The stomach. The esophagus ends in the stomach, a collapsible, 
saclike enlargement of the alimentary canal, which serves as a 
temporary receptacle for food. When contracted, the shape of 
the stomach is comparable to a sickle blade or a sausage. When 
distended with food, it is more pouchlike. The stomach has two 
openings ; one where the esophagus joins it, known as the cardiac 
opening, the other which communicates with the small intestine 
and is known as the pylorus (gateway). Both the cardiac and 
pyloric entrances are guarded by ringlike muscles known as 
sphincters. These muscles contract and keep the openings closed, 
except when food is passing through them. Food is kept in the 
stomach until it is ready for intestinal digestion ; then the circu- 
lar fibers guarding the pyloric valve relax. 

The walls of the stomach are made of muscle and other tissues. 
The inner coat (mucous membrane) of the stomach is honeycombed 
by tiny, shallow pits, which are the openings or mouths of the 
gastric glands from which the gastric juice is discharged. The 
gastric or digestive juice is composed of water, hydrochloric acid, 



and the enzyme, pepsin. The meat known as tripe is the lining 
of a cow's stomach and somewhat resembles the lining of the 
human stomach. 

Problem. What is the effect of gastric juice on protein f 

I. Prepare some very thin slices of hard-boiled white of egg. Put a slice 
of this into each of four test tubes. Have the pieces alike in size. Add to the 
four tubes the following liquids : 

A. Water, to tube number one. 

B. Water in which pepsin has been dissolved, to tube number two. 

C. Water and very dilute hydrochloric acid, to tube number three. 

D. Water, very dilute hydrochloric acid, and pepsin (artificial gastric 
juice), to tube number four. Place all four test tubes and contents in a 
warm place or in an incubator. 

II. Compare the appearance of the egg in the four tubes at the end of one, 
two, four, eight, and twenty-four hours. What effect have the various con- 
stituents of gastric juice on protein ? 

III. Give your explanation of the following : 

A. When people are suffering from indigestion, why are pepsin and 
hydrochloric acid sometimes prescribed ? 

B. If there is too much hydrochloric acid in a person's stomach, why 
is bicarbonate of soda sometimes prescribed ? 

C. Why is it unwise for a person to take artificial gastric juice or 
bicarbonate of soda unless a doctor definitely prescribes it ? 

Problem. What is the effect of the size of protein food on the time 
needed for digestion f 

I. Place in a test tube some finely chopped white of egg. Put into an- 
other test tube some larger pieces of white of egg, and into a third test tube, 
some very large pieces of white of egg. Cover the egg white in each tube with 
artificial gastric juice. 

II. Compare the appearance of the egg in the three tubes, hour by hour, 
and note the results. 

III. What do you find to be the relation of the size of food to the time 
needed for digestion ? Of what value is thorough mastication of food ? 



Problem. What animal proteins are digested most quickly and most 
thoroughly f 

I. Put into separate tubes equal-sized, thin slices of the following proteins t 

A. Well-boiled beef. • D. Roast pork. 

B. Raw beef. E. Roast lamb. 

C. Roast beef. F. Fried fish. 

Pour an equal amount of the artificial gastric juice into each tube. Place 
the tubes in a warm place. 

II. Compare at regular intervals the amounts of protein in each tube. 

III. State your conclusion from your observations. 

opening into 
the stoiScNtK- 

Secretion of gastric juice. The secretion of gastric juice is 
continuous. Even when one is not eating there is a small amount 
of secretion, but during 
the act of eating and 
throughout the entire 
period of digestion, the 
rate of secretion is greatly 
increased. This rate is 
regulated by several fac- 
tors : (1) Psychical stimu- 
lations are brought about 
by the sensations of eat- 
ing. The taste and odor 
of food stimulate the be- 
ginnings or receptors of 

Certain Sensory nerves Sit- In a gastric gland certain cells secrete pepsin, while 

certain others secrete hydrochloric acid. With water, 

Uated in the mouth and these substances are the main constituents of gastric 

rr , 1 . . . juice which is emptied from the gland into the stomach. 

nose. Inis stimulation 

results in activating the gastric glands. It has been demon- 
strated, experimentally, that as soon as a dog tastes, smells, or 
sees food, the flow of gastric juice increases. A psychic stimu- 
lation results in a copious flow of gastric juice. Such a stimula- 
tion is always brought about when one eats appetizing food. 

cells -which 
secrete ^ . . _ 
fluid containing 

neclc of 



(2) Chemical stimulation is brought about by the materials con- 
tained in certain foods and by the stimulating materials contained 
in the products of digestion. Certain foods such as meat juices 
or extractives, by their actions upon the nerves of the stomach, 
stimulate the gastric glands to pour forth their secretion. Such 
substances are called secretagogues. Other foods such as milk and 
bread do not seem to contain these substances. When these foods 
are eaten, the secretion of juices is probably due to a mechanical 
stimulus resulting from the presence of food in the stomach. When 
certain digestive products are formed, they, in turn, stimulate a 
further secretion of gastric fluid. The amount of secretion de- 
pends upon the quantity and nature of the food to be digested. 

Gastric juice is a thin, nearly colorless liquid with an acid 
reaction. It contains some inorganic salts, but the essential con- 
stituents are hydrochloric acid and two enzymes, pepsin and rennin. 
Hydrochloric acid in normal gastric fluid is found in the propor- 
tion of 0.2 to .5 per cent. Experiments have shown that a higher 
concentration of hydrochloric acid is not favorable for the diges- 
tive action of pepsin. It has the following functions : (1) it acti- 
vates the pepsinogen (an inactive form of pepsin) of gastric 
juice to form pepsin; (2) it provides an acid medium which 
is necessary for the pepsin to carry on its work; (3) it swells 
the protein fibers, thus providing a larger surface for the action 
of pepsin; (4) it kills many bacteria that enter the stomach; 
and (5) it helps to regulate the opening and closing of the pylorus. 

Pepsin, which may be called gastric protease, is first formed by 
the gastric glands as pepsinogen and is changed into pepsin when 
it comes into contact with the hydrochloric acid. It has the 
power of changing proteins into the intermediate products called 
proteoses and peptones. These are a simpler form of proteins, but 
not yet simple enough to be absorbed. Therefore, they are called 
intermediate products of digestion. 

Rennin, another enzyme found in gastric juice, acts upon casein. 


the protein of milk. It converts this substance into a clotted mass, 
the curd. The pepsin carries on the digestion of curd more effi- 
ciently in this form than it ^.Car^ioc ojxming-| 
could in the original form. y\ 

Food is kept in constant Y^|l--'Fun^.us 

motion in the stomach. J?? 4? 

By means of the action of ^ jt: \*y 
the stomach muscles, food ^w^^v' lorus ^ 
is churned back and forth 

, , , ., . The diagram on the left shows the shape of the 

and Up and dOWn Until it stomach when empty; and the one on the right shows 
i i , in the approximate shape after a hearty meal. 

is reduced to much finer 

particles than were formed in the mouth. The partially digested 
food is in liquid form and is called chyme. The reduction of the 
food into these very fine particles is invaluable in increasing the 
amount of food surface to be exposed to the action of digestive 
juices in the small intestines. The cardiac sphincter prevents the 
return of food to the gullet during the churning process. At 
intervals the pyloric sphincter opens and some of the chyme is 
forced into the small intestine by a wave of contraction. 

The stomach acts as a reservoir, holding the food and feeding it 
at regular intervals to the small intestine. The time required for 
gastric digestion of a meal depends upon the quantity and kind of 
food eaten. An average meal requires about five hours for gastric 
digestion. Solid particles tend either to keep the pyloric valve 
closed, or to force it to relax, because of fatigue, before the food 
has reached a semi-fluid condition. It is largely the acidity of the 
chyme that causes the relaxation of this valve, but in the small in- 
testine the acid has just the opposite effect. When the acidulous 
chyme passes into the intestine, it causes the sphincter to contract. 
The pylorus then remains closed until the acid has been neutral- 
ized by the alkalinity of the intestinal juice. Since few enzymes 
are produced in the stomach and their digestive action is incom- 
plete, the digestion of the nutrients continues in the small intestine. 





The salivary digestion of starch continues in the stomach until 
the acid permeates all parts of the food mass. Proteins are the 

nutrients chiefly affected 
in gastric digestion, but 
even their digestion is 
incomplete. Many bac- 
teria that enter with the 
food are killed by the 
germicidal action of the 
hydrochloric acid. 

The small intestine. 
The small intestine is a 
narrow, tubular organ . 
about one inch in diam- 
eter and from twenty to 
thirty feet in length. It 
is so coiled that it easily 
fits into the central part 
of the abdominal cavity. It is continuous with the pyloric end of 
the stomach. A membrane, the mesentery, attaches the coils of 
the intestine to each other and to the backbone. 

The small intestine has muscles which permit two kinds of 
movement, one called rhythmic segmentation and the other peri- 
stalsis. The rhythmic segmentation is caused by local constric- 
tions of the intestinal wall at regular intervals. These constrictions 
divide the chyme into a number of equal parts. Within a few 
seconds, each of these portions is halved and unites with the cor- 
responding halves of the adjacent segments. In the next con- 
striction the segments are restored to their original position. This 
enables the mass to be thoroughly mixed with the digestive juices. 
Then a peristaltic movement, a succession of waves of contraction 
and relaxation, beginning at the anterior end of the small intestine, 
sweeps along, forcing the food onward through the tube. 

Rhythmic constrictions of the walls of the small in- 
testine break the food into equal segments. Each of 
these segments is halved and unites with the adjacent 
half of the next segment. Segmentation continues, in- 
suring the complete mixture of digestive juices and food. 



Certain glands in the lining of the intestine secrete a juice called 
succus entericus or intestinal juice. Near the region where the 
small intestine leads from the stomach is the opening of a duct 
formed by the union of ducts from the liver and pancreas. 
Through this duct, juices from the liver and pancreas are emptied 
into the small intestine, where they mingle with the secretions of 
the intestinal glands. 

The pancreas. The pancreas is a flat, pear-shaped gland, about 
five inches in length, that lies slightly back of the stomach, between 
the lower part of the stomach and a fold of the intestine. It 
secretes an alkaline digestive juice called pancreatic juice. This 
juice contains three enzymes : (1) An amylase, amylopsin, similar 
to the ptyalin of the saliva, continues the conversion of starch 
into simple sugars. (2) A protease, formed as trypsinogen, is con- 
verted into trypsin by the action of a substance, enterokinase, 
secreted by the mucous membrane of the small intestine. Tryp- 
sin, similar to, but more powerful than pepsin, changes the pro- 
teins into the simpler products, peptones and amino-acids. (3) A 
lipase, steapsin, breaks down fats into fatty acids and glycerol. 
Some of these fatty acids then combine with the alkaline salts, 
present in the juices of the intestine, to form soaps. Fats are 
insoluble, but these soaps are readily soluble in water. Soap- 
making, saponification, is part of the digestive process. The 
breaking down of the fats and the saponification that follows are 
made easier by emulsification, that is, the breaking up of the fat 
into very tiny particles. 

Problem. What is the effect of an alkali on a fat ? 

Place in each of two test tubes a small amount of olive oil. Add an equal 
amount of sodium hydroxide (an alkaline material) to the oil in one of the 
tubes. Let it stand for forty-eight hours, shaking occasionally. 

I. What difference do you observe between the oils in the two test tubes ? 
The change you have brought about in the one is called an emulsion. 

II. Mount a drop of oil under the microscope. 




III. Mount a drop of the emulsified oil under the microscope. 

A. Describe the difference in the appearance of the two drops of oil. 

B. Why would you expect emulsification to hasten the digestion of fats ? 

IV. Bile and succus entericus are alkaline liquids. What effect would you 
expect them to have on the digestion of fat ? 

The liver. The liver is the largest gland in the body. It is 
situated on the right side of the body, and covers part of the 

stomach, small intestine, 
and large intestine. The 
upper surface fits closely 
into the under surface 
of the diaphragm. The 
liver secretes an alkaline 
juice, yellowish-green or 
brown in color, called 
bile. This pours, by 
means of the bile duct, 
into the small intestine 
only during the period 
of digestion. The alkali 
in the bile activates the 
digestion of fats and helps in the absorption of digested fats. The 
excess bile passes through another duct into the bile sac or gall 
bladder, where it is stored until needed. Sometimes a part of 
the bile substance crystallizes in this duct, forming gallstones. 
In such a case, the bile duct is closed and the excess bile passes 
into the blood, causing jaundice. 

Intestinal digestion. The presence of food in the small intes- 
tine stimulates the flow of intestinal juice which contains a num- 
ber of enzymes. An intestinal protease, erepsin, helps to convert 
the proteoses and peptones formed in the stomach into the end 
products of digestion, amino-acids. Several inverting enzymes 
in the intestinal juice convert the double sugars into single or 




Not far below the stomach, a tube empties into the 
intestine. This tube leads from the pancreas, the liver, 
and the gall bladder, and drains juices into the intestine. 



simple sugars. Some of these enzymes complete the digestion of 
starch and sugar which was started in the mouth. Another con- 
stituent, enterokinase, causes the trypsinogen of pancreatic juice 
to form trypsin. There is also an active hormone, secretin, in the 
intestinal juice. It has no digestive action but passes into the 
blood stream and is carried to the liver and the pancreas, which 
it activates. (A hormone is a chemical substance formed in one 
part of the body and activating another part.) It has been 
found that if a dog is fed and some of its blood in the vein lead- 
ing from the intestine is introduced into the blood of another 
dog, the liver in the second dog immediately secretes a large 
amount of bile, and the pancreas secretes pancreatic juice, which 
shows that a hormone must have passed through the blood 
and was carried to the pancreas and the liver. In the human 
body, most of the food is digested in the small intestine because 
the food stays there longest. It has been estimated, from obser- 
vations, that the last food of 
a meal passes out of the small 
intestine about ten hours 
after eating. There are more 
enzymes in this part of the 
digestive tract than in any 
part of the canal, which, also, 
accounts for the large amount 
of digestion that occurs here. 
The large intestine leads 
from the small intestine. It 
is about five feet long, and 
about two and one half inches 
in its broadest part. A little 
pouch is formed where the large intestine connects with the small 
intestine. Leading from this pouch is a short, narrow, wormlike 
tube, usually less than the diameter of an ordinary lead pencil, 



Enough of the small intestine and large intes- 
tine are shown to make clear the position of the 
appendix. Note the opening of the appendix. 




Gland or 



Place of 


Substrate 2 

End Product 8 


(alkaline) 4 


Mouth and 


Dextrins and 



A. Protease 

B. Rennin 

C. Hydro- 


A. Protein 

B. Casein 
of milk 

Q. Mineral 
matter . 


A. Proteoses and 

B. Curd 

C. Solution of 



A. Protease 

B. Amylase 


A. Proteins 

B. Starches 

■ • • .lapTi 

A. Amino-acids 

B^ Dextrins and 

*mm£p maltose 

'C. Fatty acids 
and glycerol 

D. Soaps 

opsin) * — 

C. Lipase 
sin) * 

D. Alkaline 


C. EmulsifleV 

D. Fatty acids 



Alkaline salts 


Helps to emulsify fats; saponify fatty 
acids forming soaps. These soaps 
emulsify more fats. 





A. Entero- 


B. Protease 

C. lnvertases 

a. Maltase 

b. Sucrase 
o. Lactase 

D. Alkaline 


A. Trypsin- 

B. Proteoses 
and pep- 
tones (from 


a. Dextrins 
and maltose 

b. Sucrose 
0. Lactose 

D. Fatty acids 

A. Trypsin 

B. Amino-acids 




6. Glucose and 

o. Glucose and 

D. Soaps 

1 Digestant is a term used to designate a chemical material which brings about a change In the digestive process. 

2 Substrate is a term used to designate the material changed in the process of digestion. 

8 End product denotes the product at the termination of the particular process considered. This product may 

or may not be ready for absorption. 
* There is a maltase in saliva which converts small quantities of maltose into glucose. 


called the vermiform appendix. It has no useful function. If 
food collects in the appendix, it is not easily drained out. This 
food may decay, which causes an inflammation commonly known 
as appendicitis. 

The large intestine is divided into the ascending colon, trans- 
verse colon, descending colon, and sigmoid flexure (see page 119). 
The colons and the sigmoid flexure inclose the folds of the small 
intestine. The sigmoid flexure ends in the rectum. The rectum 
is six to eight inches long and leads into the anal canal, having 
an external aperture, the anus. This opening has an internal 
sphincter muscle of the involuntary type, and an external sphinc- 
ter that is voluntary. These sphincters control the passage of solid 
waste from the body. 

The process of digestion is continued to a slight degree in the 
large intestine, due to the presence of the digestive fluids with 
which the food became mixed in the small intestine. The indi- 
gestible waste materials associated with all foods, are removed 
from the body through the large intestine by means of peristaltic 
.movements. The chief waste product is the cellulose of vegetable 
food and the fiber of meat. 

Bacteria are abundant in the large intestine. They cause the 
putrefaction of unabsorbed proteins. Some of these products of 
putrefaction are absorbed from the intestine by the blood, while 
the others are eliminated from the body. If an excessive amount 
of toxic products from this putrefaction is absorbed into the blood, 
a headache or feeling of lassitude will usually result. Normally, 
the rectum is empty until just before defecation or the elimination 
of solid waste. 


After foods have been refined, split, and standardized in the 
digestive process into the simplest forms; namely, amino-acids 
from proteins, glucose and galactos from carbohydrates, and fatty 



acids, glycerol, and soaps from fat, they are in a diffusible form 
and may enter the blood where they will be utilized. The process 
of food passing through the lining of the alimentary canal and 
through the walls of the blood vessels is called absorption. Ab- 
sorption is a process of osmosis. Very little absorption takes place 
in the mouth, throat, gullet, and stomach because the food is in 
mm *&z ■"' constant motion, and because very 

little of it has reached the end 
point of digestion. 

Most absorption takes place in 
the small intestine for the follow- 
ing reasons: (1) The digestion of 
most of the food has been com- 
pleted. Many of the end products 
of the digestive process are formed 
in the small intestine. (2) The 
great length of the small intestine 
gives a larger absorbing surface. 
(3) The small intestine is narrow 
and the food is pressed against all 
its surfaces. Consequently, not only the lower surface but all its 
surfaces are used in the absorbing process. (4) Muscular activity 
helps the food to mix with the digestive juices so that complete t 
digestion takes place. At the same time, the food is pressed against 
the absorbing surface. (5) There are special adaptations, folds, 
and villi, for increasing the absorbing surface. The length of the 
small intestine is at least twenty feet in an adult. The number 
of epithelial cells used in absorption is tremendously increased by 
the presence of circular folds or ridges around the circumference of 
the lining of the intestine. On these ridges are little structures 
called villi, so numerous and so close together that they resemble 
the nap on carpet. Each villus consists of an outer layer of epi- 
thelial cells inclosing a network of capillaries and a central lymph- 

Hairlike microscopic structures known 
as villi are found in great numbers on the 
lining of the small intestine. They in- 
crease the absorbing surface. The mouths 
of intestinal glands show among them. 




mucus cell 


channel called a lacteal. The spaces among the capillaries, lac- 
teals, and epithelial cells are filled with fluid known as lymph. 
The digested food is absorbed 
by osmosis through the epithe- 
lial cells of the villi. These villi 
cells exert a selective action, per- 
mitting only the passage of cer- 
tain materials. The process of 
osmosis here is an active not a 
passive one. Some soluble salts 
are readily absorbed, while 
others like tartrates, citrates, 
and calcium salts cannot pene- 
trate the epithelial cells. Fatty 
acids, glycerol, and soaps enter 
the epithelial cells, and during 
the process of passing through 
them are change back into fat 
particles. This fluid or lymph 
then passes into the lacteal s and 
through other lymphatics, 
leading from the lacteals, 
and eventually drain into 
the blood system. The 
amino-acids, simple sugars, 
salts, and water pass di- 
rectly from the epithelial 
cells of the intestine into 
the capillaries and thus 
become part of the liquid 
portion of the blood. 

The adaptations of the 
small intestine are so adequate that practically everything dif- 



The villus is adapted for absorption. A network of 
microscopic blood vessels absorbs digested food from the 
small intestine. A lymphatic, known as a lacteal, rims 
through the center and takes in the digested fat. 




fusible has been absorbed by the time the residual material enters 
the large intestine. This material consists chiefly of indigestible 
substances and some water. The water is gradually absorbed 
during the progress of the chyme along the large intestine. This 
results in the waste material becoming more and more pasty as it 
approaches the rectum for elimination. 

Hygiene of digestion. The body is normally in a state of health 
and not disease. It is abuse of some kind that induces digestive 
disturbances commonly called indigestion. Hygienic habits of 
living make for good digestion. Activity in the open air and sun- 
light, good food, relaxation, and rest are of prime importance. 
Proper nutritional habits should, be established. Meals should 
be taken at regular intervals. If the digestive organs are worked 
periodically, more regular digestive habits are established. As a 
rule, food should not be eaten between meals, for it disturbs the 
physiological routine and, also, interferes with the appetite. 

Since the alimentary canal is composed largely of muscles, exer- 
cise is invaluable in keeping these muscles in proper tone. By 
tone we mean the constant and unconscious tendency of the 
muscles to contract under normal conditions. However, strenuous 
exercise immediately after a meal is bad, as it withdraws much of 
the blood from the digestive organs where it is needed, and sends 
it to the active skeletal muscles that are working. This may re- 
sult in indigestion and possibly muscular cramps. Consequently, 
neither maximum digestion nor proper muscular activity is ob- 
tained. This is one reason why persons are subject to digestive 
or muscular cramp if they swim too soon after eating a heavy 
meal. For a similar reason, undue excitement or mental stress 
should be avoided during or after meals. Since the stimulation 
of digestive glands is partly psychic (mental), violent emotions in- 
terfere with the proper flow of digestive juices and withdraw the 
blood from the digestive organs and send it to the brain and 
nervous system. Pavlov, a famous Russian physiologist, learned 


through scientific experimentation, that, in dogs, fear, anger, and 
rage interfered with proper digestion and altered the character of 
the digestive juices. 

Food should be thoroughly chewed to be properly mixed with 
-the saliva. As much water as possible should be taken each day. 
There is no objection to drinking water with the meals, providing 
that it is not so cold that the organs might be chilled, and that the 
food is thoroughly masticated and not washed down by the water. 

As the undigested part of the food passes through the colon, 
it gradually loses its water through the process of absorption. 
This waste becomes semisolid. It should be removed daily at 
a regular time. If this defecation does not take place because of 
haste, or inconvenience, or some irregularity in the routine, the 
water in the solid waste becomes absorbed and the waste be- 
comes so compact that it is difficult and in some cases impossible 
to eliminate. A cathartic or laxative must then be taken to stimu- 
late the activity of the intestinal movement. It is a well-known 
fact that improper foods may cause constipation. This condi- 
tion may be avoided by eating bulky foods which will stimulate 
the work of the muscles of the canal. Such bulky foods are 
vegetables, salads, and fruits. Proper routine, including regu- 
larity of meals and regular times for elimination of wastes, must, 
also, be established. 

Laxatives are useful in removing an acute condition of constipa- 
tion but should not be taken regularly. Some laxatives contain 
drugs that stimulate the nerves controlling the muscles used in 
defecation. Other laxatives called the salines contain the salts 
of sodium, potassium, and magnesium. They cannot be absorbed 
by the intestine. They hold a great deal of water in solution and 
increase and soften the bulk of the material, favoring its move- 
ment along the canal. Epsom salts, magnesium citrate, and so- 
dium phosphate are examples of saline cathartics. A third type 
of laxatives is heavy oil, mineral or castor oil. These line the food 



tract with a film of oil. The oil tends to soften and increase the 
bulk of the intestinal content. 

The best ways of preventing and overcoming constipation are : 
to act on the desire for defecation, to have a regular time for 


830TM •Mifc.nigHC 


As digestion takes place, food is gradually absorbed until the wastes only enter the large in- 
testine. When these wastes reach the rectum, they are ready for elimination. It takes about 
twenty-four hours for digestion to be completed and for the wastes to reach the rectum. 

doing this, and to eat plenty of fruit and vegetables, as these tend 
to promote peristalsis. 

Some investigators think that one of the contributing factors to 
old age is the toxins absorbed from putrefaction in the large intes- 
tine. The toxins affect the arteries causing the hardening of the 
arterial walls. The bacteria of putrefaction work best in an alka- 
line medium. A Russian physiologist, Metchnikoff, conceived the 
idea of introducing an acid into the large intestine. He thought 
this would check putrefaction and possibly postpone old age. He 
observed that Bulgarians who used a great deal of sour milk, live 
to a greater age than other people. He knew that the' acids from 
most foods are neutralized before they reach the large intestine, 
but that unlike ordinary sour milk the acid in Bulgarian milk 
does reach the large intestine. Different strains of bacteria in 
milk cause the two different reactions. Bacillus bulgaricus and 
bacillus acidopholus which is a related strain of microorganisms, 
have been cultivated in America. Experiments are now being 
made with acidopholus milk to determine whether it does have a 
beneficial effect although there is as yet no definite proof. 

People should not become faddists in eating. Nutritional 


rules established by proper authorities should be followed. If 
one suffers from overweight or underweight, his diet should be 
regulated professionally and not by quack methods. All kinds of 
diets are in vogue; namely, milk diets, raw-food diets, cooked- 
food diets, vegetable diets, and fruit and nut diets. As a rule, 
most, if not all of these, should be questioned and avoided by 
the average person unless a competent physician has done the 
prescribing. Otherwise, a diet might be selected that would be 
detrimental rather than beneficial in many instances. The use 
of patent medicines of all kinds should usually be avoided. Some 
people decide they have too much acid in their systems and take 
an alkali like bicarbonate of soda to counteract it. In many cases, 
bicarbonate of soda stimulates the production of more acid. 
Others decide they lack gastric juice and buy artificial gastric 
juice or pepsin and hydrochloric acid to aid digestion. This may 
interfere with the proper production of natural gastric juice. Still 
others believe a physic taken once a week is invaluable. This 
may get the system so used to drugs that in time it will not be 
able to function without artificial stimulation. Headaches, due 
to digestive disorders, are cured by getting rid of the cause of the 
disturbance, not by headache powders. 

Briefly stated, normal digestion is our heritage. If habits of 
eating the proper foods and defecation are regular, digestion will 
usually be normal. The best way to clear up indigestion is to find 
out the cause of the irregularity and correct it. 

Questions and Suggestions 

1. If the kinds or classes of enzymes are amylases (starch-split- 
ting), proteases (protein-splitting), and lipases (fat-splitting), classify, 
in their right classes, all the enzymes that you have studied. 

2. Discuss the different causes for the stimulation of the flow of 
digestive juices. 

3. Discuss the importance of peristalsis in eliminating the solid 
wastes of the body. 


4. Locate four sphincters and discuss the importance of each. 

5. Plan an experiment which will illustrate the digestion of 

6. Name three intermediate and three end products in the digestion 
of nutrients. 

7. Discuss the importance of the villi in absorption. 

8. Give two classes of cathartics or laxatives. After reading the 
labels of two or three common cathartics, state to which class each 

9. Name an unhygienic condition that is frequently found among 
high school students and which may lead to digestive disorders. 

10. What is the objection to reading and eating at the same time ? 

11. Name two scientists who have investigated food habits. Dis- 
cuss their contributions to the science of nutrition. 

12. Review and report on the digestion and osmosis experiments 
set up in elementary science. 

Supplementary Readings 

Haggard, H. W., Science of Health and Disease (Harper & Brothers). 
Kimber and Gray, Textbook of Anatomy and Physiology (The Macmillan Co.). 



William Harvey. 

Vesalius' idea of blood vessels. 

What is the relation of blood to the other tissues of the body? Where is 
blood made and where are its various parts destroyed? What is meant 
by different types of blood? What is the imjwrtance of blood tests? 

Many cells are far from the source of supply of food and oxy- 
gen and far from the organs which will excrete their wastes. 
The blood, therefore, acts as a medium for the distribution of 
food materials and oxygen to the cells, and for the collection of 
wastes from the cells. 

Circulation is the ceaseless movement of blood through the 
body in a system of closed tubes called blood vessels which branch 
to all parts of the body. When blood flows from any. part of the 
body, blood vessels have been broken. 

Problem. Study of the blood. 

Secure some freshly drawn blood from a butcher or slaughterhouse. Keep 
in a tightly corked bottle when not in use. 

I. Pour two or three ounces of the blood into an open dish and beat it 
vigorously with a few broom straws. 

A. Describe the nature of the material removed by this beating. This 
material is called fibrin. As the beating exposed the blood to the air, 
the liquid blood protein, fibrinogen, was converted into the solid form, 

B. Describe the material left in the dish. This is defibrinated blood. 



II. Continue beating until no more fibrin can be removed. 

III. After beating, remove the fibrin, and pour the remainder of blood 
into a bottle. Label it defibrinated blood. 

IV. Pour a like quantity of unbeaten blood into a second bottle and let 
both volumes of blood stand, corked, for several days. Compare the appear- 
ance of the materials in the two bottles. 

A. Describe any solid mass, a clot, which may have formed in one or 
both bottles. 

B. Describe the liquid around the clot. This liquid is called serum. 
Compare blood serum with defibrinated blood. 

V. Place an ounce of blood in a third bottle and, by means of a delivery 
tube, add oxygen to it. 

A. What effect has oxygen on the color of blood? This is now oxy- 
genated blood. It may be compared to arterial blood. 

VI. Place an ounce of blood in a fourth bottle and, by means of a delivery 
tube, add carbon dioxide to it. 

A. What effect has carbon dioxide on the color of blood? This is 
deoxygenated blood. It may be compared to venous blood. 
"VTI. Look at the veins in your wrist. 

A. Do veins appear to have oxygenated or deoxygenated blood in 

B. Explain why blood which flows from a cut vein looks like oxy- 
genated blood. 

Problem. Study of blood serum. 

Test the serum for protein, starch, sugar, fat, water, and mineral matter. 
Account for the presence or absence of each. 

Problem. Study of blood corpuscles. 

Mount a tiny drop of blood on a glass slide. By means of the edge of a 
square cover glass, smear the drop across the slide, making a thin film. Cover 
with Wrights' Blood Stain for three minutes ; then wash off the stain. Exam- 
ine with low power and then with high power of the microscope. Observe the 
regular, disklike, yellowish cells which cling together ; when in masses of great 
numbers they appear red. These are the red corpuscles. The larger, irregu- 
lar, blue cells are the white corpuscles. When unstained, they are colorless. 

I. Estimate roughly, the proportionate number of the two types of cor- 


II. Suggest a reason for calling the white corpuscles the amoeboid cor- 
puscles ? 

III. State three structural differences between the red and white corpuscles. 

IV. What functions did the Amoeba perform with its pseudopodia ? Cer- 
tain white corpuscles can, in a similar manner, engulf bacteria. These bac- 
teria are then digested by the white corpuscles and are thus eliminated from 
the blood. 

Composition of the blood. Blood may be called a tissue. 
It consists of a yellowish liquid, the plasma, and cellular particles, 
the red and white corpuscles and blood platelets. The plasma 
is a clear fluid containing fibrinogen and other blood proteins, 
nutrients, and wastes. Some of the proteins in the plasma are 
peculiar only to the blood. Little is known of the use of these, 
with the exception of fibrinogen. The use of fibrinogen, which was 
transformed to fibrin in our laboratory exercises, will be discussed 
later. Amino-acids are also a part of the blood plasma. These 
amino-acids are digested proteins which are called building stones 
of the body. They are distributed by the blood to the cells, and 
they build protoplasm. Fat, glucose, water, and mineral matters 
are also taken in by the plasma from the alimentary canal. More 
than 80 per cent of the plasma is water. There is from 0.07 to 0.15 
per cent each of fat and glucose. The proteins constitute from 
6 to 8 per cent of the plasma. 

All of the food that is digested and absorbed does not circulate. 
It is either used or stored in cells and gradually returned to the 
blood as tissue cells require it. Animal cells can store fat and 
starch, but very little protein. Therefore, any extra protein eaten 
tends to be broken down and eliminated. Secretions from ductless 
glands are absorbed directly into the blood. These liquids circulate 
through the body, activating, inhibiting, or regulating the more 
remote parts. 

Oxygen is taken from the lungs by the red corpuscles of the 
blood. The wastes, carbon dioxide, water, and urea, collected from 


the different cells as the blood circulates, are dissolved in the 
plasma and carried to the kidneys, lungs, or skin, where they are 
thrown out. 

There are various kinds of white corpuscles. When stained, one type, the polymorphonu- 
clear, shows nuclei with one, two, three, four, or five enlargements. In health there is a 
definite relationship of the numbers of each of the above; in starvation or disease the fours 
and fives are seldom found. Blood tests usually indicate the general condition of the body. 

Chemical substances in blood, known as antibodies, help to com- 
bat germs directly, or neutralize the toxins which the bacteria 
secrete in the blood. These substances are produced by the cells 
during a disease or infection. Immunity to disease, which will be 
discussed later, is brought about in the body by these antibodies. 

Blood a tissue. Red corpuscles were mentioned when tissues 
were considered. They are five to seven hundred times as numer- 
ous as the white corpuscles. Present investigations show that they 
differ from other cells in that they lack a nucleus. They are made 
from living cells located in the blood-forming tissue of the mar- 
row of bones. Millions of these corpuscles are formed and given 
off into the blood each minute. They are thought to gradually 
disintegrate as they move about. The final destruction of the 
small fragments probably takes place chiefly in the spleen and the 
liver, but may occur in any part of the blood system. The correct 
functioning of the red corpuscles depends upon the haemoglobin 
which is the oxygen-carrying pigment of the blood. 

A serious decrease in the number of red corpuscles or a deficiency 
in haemoglobin in the corpuscles causes a condition known as 
anaemia. Certain types of anaemia in people have been treated 
successfully by a liver diet. The liver which is used as food 
probably contains iron gotten from destroyed corpuscles. This 
form of iron seems to be more valuable than the iron com- 
pounds in medicines used for treating anaemia. The body seems 


to be able to assimilate it better. Whether the liver diet is reme- 
dial because of the iron present, or whether there is a vitamin 
present that stimulates the body to make more red corpuscles, 
has not yet been conclusively proved. In order to determine 
whether a person has anaemia, a drop of blood is put on a slide 
which is divided into sections by marks etched on the surface. 
These spaces are called counting chambers. The number of red 
corpuscles are estimated in relation to the white corpuscles present. 
This is called a blood count. If there are too few red corpuscles 
in relation to the white corpuscles, the person is said to be anaemic. 
There is also a color scale used to test for anaemia. 

The haemoglobin in the red corpuscles readily unites with oxy- 
gen and forms an unstable compound, oxyhaemoglobin. When 
the oxygen-carriers pass cells deficient in oxygen, the oxyhaemo- 
globin will give up its oxygen supply. The red corpuscles of man 
are smaller than the red corpuscles of nearly every other animal. 
This allows a greater number per given volume and gives a greater 
absorbing surface. Thus these numerous small corpuscles carry a 
greater supply of oxygen than if they were larger. 

The white corpuscles are larger and less numerous than the red 
corpuscles. Because they are capable of independent motion, 
they can force their way among the cells, which make up the walls 
of capillaries, and escape into surrounding tissues. Certain of the 
white corpuscles, by means of their protoplasmic processes, en- 

White corpuscles can make their way among the cells in the walls of capillaries by their inde- 
pendent motion. They may be found in tissues where they can attack invading bacteria. 

gulf the bacteria in blood and other tissues, and digest them. 
These are the phagocytes and the process is phagocytosis. It is 
thought that white corpuscles originate in lymph nodes and in the 



spleen through mitotic division. When an infection occurs in the 

body, they multiply in great numbers and later disintegrate or 

probably escape from the blood upon mucous surfaces, especially 

, , in the intestine. When 


°*v££ en 


The cells take oxygen carried by the red corpuscles 
and use it to burn food for the release of energy. 

white corpuscles are de- 
stroyed by bacteria, the 
dead corpuscles are called 
pus. An abnormal in- 
crease of white corpuscles 
in the blood usually indi- 
cates the seriousness of 
the infection and the 
amount of resistance of- 
fered by the body. 
Blood clotting. Blood platelets are tiny bits of protoplasm 
found in blood. They are small cells, but lack a nucleus. Their 
origin is probably similar to the red corpuscles. They are con- 
cerned with blood clotting which takes place when blood is exposed 
to air because of wounds or hemorrhages. Blood platelets dis- 
integrate and give rise to a substance which plays an important 
part in the change of the liquid protein, fibrinogen, always present 
in blood, to a solid form, strands of fibrin. Calcium, also present 
in blood, is involved in the precipitation of the fibrinogen. The 
strands of the fibrin entangle the blood cells and form a jellylike 
blood clot. Bleeding may thus be stopped. The body then re- 
pairs, by building new cells, the blood vessels from which the blood 
is flowing. People whose blood does not clot in the normal length 
of time or who bleed profusely even from the slightest wounds are 
called bleeders. The disease is haemophilia and it is usually 

Blood grouping. The composition of human blood is constant 
with the exception of the oxygen and carbon dioxide content. 
But since the serum of one person may be injurious to that of 



another; four different groups of blood are now recognized. Under 
ordinary conditions the body can renew blood as fast as it is needed. 
However, in certain diseases and in cases of severe hemorrhages 
it is necessary to introduce a quantity of blood into the veins of 
the patients. In such cases, blood of a similar group must be 
transfused, or results may be fatal through the dissolving of the 
corpuscles, and a consequent release of a foreign haemoglobin. 
Therefore, doctors always test a donor's blood to make sure it is 
of the same group as the patient's before making a transfusion. 

Necessity for circulation. Each cell in the body has work to do. 
This work is performed through energy released in the cell. We 
have already learned that glandular cells use chemical energy, 
muscular cells use mechanical energy, and nerve cells need nervous 
energy. All of these forms of energy are obtained from the food. 
When the food is oxidized in the body, the energy stored in the 
food is released. Each cell must receive a supply of oxygen and 
food. in order to carry on the oxi- 
dation process with its accom- 
panying release of energy. When 
the food is oxidized in the cells, 
carbon dioxide, water, and ni- 
trogenous wastes are formed, 
and must be removed. The 
blood carries the oxygen and 
food to the cells and removes 
the wastes from them. Since 
the white corpuscles combat 
germs, the blood must carry a 
continuous supply of these to 
whatever part of the body that 
needs them. At the same time other protective chemical sub- 
stances, antibodies, must be carried to the places needing them. 
As food is oxidized in various tissues, heat is released. A great 

Wastes formed during oxidation reach the 
blood by means of the process of osmosis. 


deal of heat is generated in active tissues such as muscular tissue 
and the liver, and the surplus heat must be distributed to passive 
tissues. Very little heat is generated in passive tissues such as 
bone, so heat must be sent to them by the blood when needed. 
The blood system may be compared to a hot- water system. The 
muscles are like little furnaces in which burning takes place. This 
heats the surrounding blood. As the blood circulates it radiates 
heat to the tissues that need it, and thus keeps the temperature of 
the body constant at ninety-eight and six tenths degrees Fahrenheit 
(98.6° F.). When glands give off secretions and have no ducts for 
draining the secretions, the blood absorbs them. 

In brief, the functions of blood are nutritive, protective, and 
excretory. When scientists can supply the same conditions to 
tissues outside of the body as those provided by the blood, tissues 
can be kept alive under experimental conditions outside of the 
body. This was one of CarrelPs big achievements. He experi- 
mented for many years before he was able to duplicate the con- 
ditions outside of the body that were found in the blood. When 
he succeeded in doing this, he was able to grow tissues outside of 
the body. His work has been previously discussed on page 54. 


1. Define* oxygenated and deoxygenated blood. ♦ 

2. What is defibrinated blood ? 

3. Compare arterial and venous blood. 

4. Compare the red and white corpuscles in appearance, size, num- 
ber, and function. Where are they made and where are they de- 
stroyed ? 

5. Give six functions of blood. 

6. Why does blood clot ; why is blood clotting necessary ? 



An early drawing showing the 
circulation of the blood. 

Malpighi's drawing of circula- 
tion of a chick embryo. 

What are the paths of blood through the body? What causes the cir- 
culation of blood f What is the relation of circulation to the cells? 

Problem. The study of blood vessels. * 

Anaesthetize a tadpole with a little ether. Place the tadpole in a Petri 
dish in a little water so that the tail can be mounted under the low power 
of the microscope. Do not keep the tadpole out of water more than ten or 
fifteen minutes at one time. 

I. Note the blood flowing up some blood vessels and down others. 

A. Suggest a reason for the parallel arrangement of the blood vessels. 

B. Suggest a function of the connecting blood vessels. 

II. The large elliptical cells passing through the vessels are the red cor- 

A. What is the advantage of having corpuscles in the smallest blood 
vessels pass cells in a single line ? 

B. Compare the red corpuscles of the frog with those of man. 

III. Look at the sun or at a very bright light. Note tiny particles passing 
through a network of tubes in your eyes. These are the red corpuscles passing 
through tiny blood vessels. 

In the plant, a system of tubes called ducts and sieve tubes dis- 
tributes cell sap. In the human body, a network of tubes makes 
up the circulatory system for the distribution of blood throughout 
the body. Materials must enter and leave the blood by means 



of osmosis, since the blood vessels are closed tubes. Blood sup- 
plies the cells with building and fuel materials and collects wastes 
from them ; therefore, some blood vessels must be tiny enough 
to get near to all the cells. These microscopic blood vessels, the 
capillaries, connect with larger and larger vessels, the arteries and 
veins, until the largest arteries and veins attain a size of one half 
inch in diameter. 

Problem. Study of the heart. 

Secure from the butcher, the heart of an ox or of any other large animal. 
If the school is near a slaughterhouse, it may be possible to secure enough 
specimens so that each group of four students may have one. Cut the hearts 
longitudinally. (These hearts may be kept in formaldehyde for further study.) 

I. Describe the covering of the heart (the pericardium) . 

A. What is its purpose ? 

B. Explain all adaptations for this purpose. 

II. Count the number of chambers or spaces in the heart. 

A. The upper spaces are the right and left auricles; the lower spaces, 
the right and left ventricles. 'Describe the structure, location, and size of 
auricles and ventricles. 

B. Describe the structure that separates the left side of the heart from 
the right side. 

C. Find the movable flaps, known as valves, that separate the auricles 
from the ventricles. 

1. Describe the valves in the left side of the heart, including in 
your description the number of flaps, method of attachment, and func- 
tion. Observe and describe the valves in the right side. 

a. When blood passes from the auricles to the ventricles, what 
effect would you expect it to have On the valves ? 

b. If blood attempts to pass from the ventricles to the auricles, 
what effect would it have on the valves ? 

c. What must be the normal direction of the flow of blood ? 

III. Name the tissues that largely comprise the walls of the heart. 

A. Compare the thickness of auricle walls with those of the ventricle. 

B. Compare the thickness of the wall of the left ventricle with other 
walls of the heart. 

C. What is the relation of thickness of heart muscle to its activity ? 


IV. Find the large vessel coming up through the center of the heart. If 
enough of it is still attached, it will be seen to curve around in back of the 
heart. Put the wooden end of your needle through it. 

A. Into what chamber does the needle penetrate ? This vessel is an 
artery known as the aorta. It sends blood by means of branches to every 
part of the body except the lungs. 

B. Describe the walls of the aorta. 

1. Suggest a reason why arteries hold their shape instead of col- 

2. Suggest a reason why they were originally named arteries (aer 
— air ; terin — to hold) . 

V. Locate two large vessels leading into the right auricle. These are 
two veins called the upper or superior vena cava and the lower or inferior 
vena cava. They bring blood from all parts of the body, except the lungs, to 
the heart. 

A. Compare the walls of these veins with the walls of the aorta. Which 
are capable of greater movement ? Why ? 

B. What is a probable difference in function between the inferior and 
superior vena cava ? 

C. Suggest a reason why veins do not hold their shape when empty of 

VI. Try to locate the pulmonary artery originating in the right ventricle 
and the four pulmonary veins leading to the left auricle. The pulmonary 
artery takes blood from the heart to the lungs ; the pulmonary veins convey 
blood from the lungs to the heart. 

A. Suggest a reason for the blood going to the lungs. 

B. Suggest a reason for the blood returning from the lungs. 

VII. Make a simple diagram of the heart and the blood vessels connecting 
with it. Label right auricle, left auricle, right ventricle, left ventricle, septum 
or partition, valves, aorta, superior vena cava, inferior vena cava, pulmonary 
artery, and pulmonary veins. 

VIII. Write a brief paragraph describing the structure of the heart. 

The organs of circulation. The arteries, veins, capillaries, and 
heart make up the circulatory system. Approximately in the 
center of the chest cavity, with its apex pointing toward the left, 
is the conical-shaped heart. It is a highly muscular organ pro- 

WH. FITZ. AD. BIO. — 11 


tected from friction by the moist membranous pericardium which 
covers it. The ribs and breast bone furnish protection against me- 
chanical injury. Large blood vessels collect blood from all parts of 
the body and return it to the heart ; others take blood from the 
heart to all parts of the body. The heart tissue, itself, has an in- 
dependent blood supply called the coronary circulation. When the 
heart is cut longitudinally, it is found to consist of four chambers, 
a left auricle, a right auricle, a left ventricle, and a right ventricle. 
A thick muscular partition through the center of the heart sepa- 
rates the left side from the right side. The auricles receive blood 
from the veins and give it to the ventricles. The act of receiving 
blood does not require much work, so the auricle walls have com- 
paratively little muscle in them. The ventricles force the blood 
into the arteries to all parts of the body. In order to ac- 
complish this pumping, the ventricles have very thick muscu- 
lar walls. The walls of the left ventricle are much thicker 
than the walls of the right ventricle. They have to send 
blood to all parts of the body while those of the right ventricle 
merely send blood to the lungs. Separating the ventricles from 
the auricles are trapdoor arrangements called valves. These 
are made of very strong connective tissue attached by cords of 
the same tissue to the ventricles. On the left side, there is a 
valve with two flaps, and on the right side, a valve with three 
flaps. The blood passes from the auricles to the ventricles, by 
merely pushing against the valves. If the blood backs up during 
the contracting of the ventricles, the valves fill up, close, and 
prevent the return of the blood into the auricles. Thus the 
blood is kept moving in only one direction. 

Arteries. The tubelike blood vessels which carry the blood 
from the heart to all parts of the body are called arteries. The 
largest ones branch from the ventricles, and subdivide into smaller 
vessels until a network of very fine tubes, practically microscopic, 
is formed. These connect with the capillaries. The arteries can 


to K^clSL- 



to "heocol 


A diagram of the circulatory system in which the blood vessels containing arterial blood are 
colored red, those containing venous blood are colored blue, and the lymphatics are yellow. 
Note that, in general, only the arteries contain arterial blood, but the veins coming from the 
lungs have received a new supply of oxygen and hence also contain oxygenated blood. 



usually be distinguished from veins and capillaries by the presence 
of considerable muscular tissue in their walls. Early anatomists, 
when dissecting bodies, found these tubes empty and thought 
that they were supposed to carry air and therefore called them 
arteries (air-tubes) . Even the smaller arteries have muscular walls 
and can contract and relax. The aorta and its branches are full of 
blood all the time. When the left ventricle contracts, the blood 
cannot move forward into the comparatively narrow arteries fast 
enough to make room for the new supply sent out by the ventricle. 
But, due to the elasticity of its walls, the aorta can expand and 
receive the incoming blood. The impulse of the blood sent into the 
arteries by the ventricular contraction causes a wave of distention 
to travel along the blood vessel. This wave of distention is called 
the pulse. The pulse is the passive stretching and contracting of 
the elastic tissue. If an increased amount of blood is sent to a 
particular part of the body, at any time, the arteries can always 
accommodate it because of the elasticity and muscularity of their 
walls. The pulse may be felt wherever an artery comes near the 
surface of the body. Most arteries are deeply embedded in other 
tissues so that the pulse is not easily noted. Arteries run near 
the surface in the wrists, neck, and temples. Probably the most 
convenient place for taking a pulse is in the wrist. 

Problem. Study of the pulse rate. 

I. Place the middle finger of the right hand about two inches from the ball 
of the thumb of the left hand, thus locating a pulse. Count the number of 
beats felt per minute. This is called taking the pulse rate. 

II. Run up and down stairs two or three times. Again take the pulse rate. 

A. What effect has exercise on the pulse rate ? 

B. Keeping in mind the fact that the walls of the heart and arteries 
have large deposits of muscle and elastic fibers, give the reason for the 
effect of exercise on the pulse rate. 

C. Discuss the beneficial effects of exercise on the arteries. 

D. If you get insufficient exercise, what effect would it eventually 
have on the heart and arteries ? 



III. Lie down or sit quietly for two or three minutes. Again record the 
pulse rate. 

A. What is the effect of rest on the heart and arterial muscles ? 

IV. What is the value of the arterial pulse ? 

V. If more blood is needed in one part of the body than in another, how can 
it be properly distributed ? 

The normal pulse rate in men is seventy-two beats per minute, for women 
seventy-six. The pulse rate is still higher in children. An abnormal pulse 
indicates some sort of unusual physiological condition. 

Capillaries. The capillaries are microscopic tubes found 
among the cells of the tissues. These vessels are characterized 
by a lack of muscular tis- 
sue. Their walls are mem- 
branous. They receive the 
blood from the arteries 
and send it to the veins. 
Materials pass from the 
blood through the thin 
walls of the capillaries to 
the cells in surrounding 
tissues. The waste prod- 
ucts in the lungs and 
other parts of the body 
pass into the blood from 
which they are later dis- 
charged. This inter- 
change of products is 
possible because of the 
membranous walls of the 
capillaries. The blood receives enough of an impulse from the 
heart to keep it moving through the capillaries. 

Veins. The veins receive the blood from the capillaries and return 
it to the heart. The veins connected directly with the capillaries 

Capillaries are so tiny and numerous that they 
traverse the most minute parts of the body. The red 
corpuscles pass through in practically single file. 



are very tiny in size, 
them join together. 

n TO n 

Blood flowing through veins passes 
valves. When these valves are 
opened due to back pressure, the 
blood finds other vessels, sometimes 
smaller, to traverse. 

They get larger and larger as numbers of 
The largest ones empty into the heart. 
Their walls are composed of elastic, 
connective, and some muscular tissue. 
There might be a back-flow of blood 
in the veins were it not for the 
valves that are found along the walls 
of the veins. These open in the 
direction of the blood flow which is 
toward the heart. If blood tends to 
flow back, they open, and prevent the 
blood from moving in the opposite direction. These valves may 
be seen if you let your hand hang down, and shut off the blood 
supply by holding the wrist tightly. The blood will back up 
against the mouth of the valves and open them. As blood fills 
these valves, a slight distension of the vein will be noticeable. In 
some older people, these valves are likely to thicken and show as 
swellings on the body. Since so small an amount of muscular tissue 
is present in the walls, very little muscular contraction is possible. 
The movement of blood in 

the veins is caused by the 

heart which is aided greatly 

by the valves in the veins, 

by muscles, and by the 

lungs. The network of 

capillaries feeding the veins 

increases the flow just as 

tributaries to a river cause 

the flow of water in the 

river. As breathing takes 

place, pressure on the large 

veins in the chest is released. This causes the blood to flow up 

through the veins. Skeletal muscles in all parts of the body 

The valves in veins are like tiny watch-pockets. If 
blood tends to flow back, the valves fill up and close 
the passage; thus blood is kept moving in one direction. 




One blood vessel leads directly into another. The structure of 
their walls varies, however. The small, muscular-walled arteries 
lead into the membranous capillaries which, in turn, lead into the 
smallest of the veins. 

squeeze the veins as they contract. This, too, forces the blood 
onward. If a person is inactive . for a long time, the blood in 
the veins becomes sluggish. When we sit still for too long a time, 
we say a foot has 
" gone to sleep." 
Other signs of 
discomfort may, 
also, be evident 
because the skele- 
tal muscles are 
not propelling 
the blood through 
the veins. 

Course of the 
blood. The sys- 
temic circulation. 
The circulation of the blood through the body is easily under- 
stood and remembered if we keep in mind that the sequence 
of organs is from the left ventricle, arteries, capillaries, veins, 
and right auricle. Blood never returns directly to the same 
side of the heart it left and the auricles do not connect with 
each other, nor do the ventricles connect with each other. 

The left ventricle contracts and sends the blood past the valves 
into the large artery called the aorta. This, in turn, contracts 
and sends blood through smaller and smaller arteries to all parts 
of the body except the lungs. As the arteries get in among the 
tissues of the body, the muscular tissue decreases until the walls 
of the blood vessels consist of a single layer of cells. • These ves- 
sels are the arterioles which terminate in the capillaries. After 
giving up the needed materials to the cells through the walls of 
the capillaries and collecting excretions from the cells, the blood 
passes into tiny veins. As the small veins lead from the tissues 
they join and increase in size until they form the two largest 



veins in the body. The veins from the organs below the heart 
drain into the lower or inferior vena cava; the veins from 
the organs above the heart, with the exception of the lungs, 
lead into the upper or superior vena cava. Both of these large 
veins empty into the right auricle. From there, blood passes 
to the right ventricle. This completes the systemic circula- 
tion. The systemic circulation enables the blood to supply 
tissues with needed materials and collect excreted materials from 

The pulmonary circulation. The right ventricle contracts and 
sends the blood into the pulmonary artery which divides into two 
sets of branches, one set going to each lung. In the lungs, these 
arteries get smaller and smaller until they lead into the capillaries 
of the lungs. . The carbon dioxide, collected from the cells, is 
given to the lungs and a new supply of oxygen is absorbed through 
the capillary walls. The blood then travels through veins of in- 
creasing size until it reaches the large pulmonary veins, which take 
the blood to the left auricle. This is called the pulmonary or 
lung circulation. The pulmonary circulation enables the blood to 
give up the carbon dioxide and take in a new supply of oxygen. 

The portal circulation. 
As the blood passes 
through capillaries in the 
stomach and small intes- 
tine it absorbs food that 
has been digested and 
standardized into end- 
products. Were all this 
collected food to circulate 
until utilized the amounts 
of nutrients in the blood 
would vary considerably. The nutrients in the blood are kept 
constant to a large extent by the activity of the liver. The 

The passageway between the left auricle and 
left ventricle is guarded by a mitral, two-cupped valve. 
The passageway between the left ventricle and the 
aorta is also guarded by a valve. By their action, 
valves allow the blood to flow in only one direction. 



stomach, small intestine, spleen, and pancreas receive blood from 
the capillaries in those organs and send it to a large vein called the 


amphibian reptile. 


Among the vertebrates, animals are found with different numbers of chambers in the heart. The 
heart of mammals is really two separate hearts, each composed of an auricle and a ventricle. 

portal vein. This vein breaks up into capillaries in the liver. By 
means of osmosis the liver cells either take out excess nutrients or 
give needed sugar to the blood. Another vein, the hepatic vein, 
then carries the blood with its normal content of nutrients to 
the inferior vena cava. It takes, approximately, thirty seconds 
for the blood to make a complete circulation. - 

Functions of the liver. The liver, like all other organs, con- 
sists of cells. These cells use oxygen and food and give up carbon 
dioxide, water, and urea. The partially disintegrated red cor- 
puscles are completely destroyed in the liver. The liver uses some 
of these corpuscles and other substances as a basis for the manufac- 
ture of bile. The function of bile was discussed in a former chapter 
(page 132). Excess glucose is stored in the liver in the form 
of glycogen or animal starch. When the cells of the body need 
sugar, this glycogen is ^converted back into glucose and absorbed 
again by the blood. Protein is not stored in animal cells ; there- 
fore, excess proteins must be destroyed. This destruction is ac- 
complished mainly by the liver. The carbon, hydrogen, and oxygen 
are taken from the protein or amino-acid and stored as glycogen. 
Through an oxidation process, urea is formed in the cells from the 
nitrogen, sulphates from sulphur, and phosphates from phosphorus. 
These are given into the blood and are extracted by the kidneys. 



Blood Givks 

Blood Takes 

Skin . . . 

Water, organic salts, urea, excess 

Lungs . . . 

Carbon dioxide, water 


Kidneys . . 

Water, urea 


Materials for making digestive 

Secretin, digested nutri- 

intestine . 


ents, water 

Liver . . . 

Excess protein, excess sugar, 

Needed sugar, urea, excess 

secretin, worn-out red cor- 

sugar, and organic sub- 

puscles, materials for manu- 


facture of bile 

Blood functions. As the blood circulates through the various 
organs of the body, it gives up certain materials and takes in others. 
Those functions that take place in all cells are called general func- 
tions; those peculiar to any organ are called specific functions. 
Assimilation and oxidation are activities performed in all cells; 
therefore, they all need food and oxygen and all give up carbon 
dioxide, water, and urea to the blood. These are known as 
general functions. Since each organ has a special work, there are 
certain activities performed by the blood in relation to these 
particular functions. In the above table a list is shown of special 
work carried on by the blood in some of the organs. 

Questions and Suggestions 

1. Compare arteries, veins, and capillaries as to (a) position, (b) size, 
(c) structure, and (d) function. 

2. Explain how to take a pulse. 

3. Trace a complete circulation, naming, in order^ all the blood ves- 
sels traversed from the time the blood leaves the left ventricle until it 

4. What is the function of each of the systems of circulation : (a) sys- 
temic, (6) pulmonary, and (c) portal. 



Lymph tubes. 

Enlarged lymph gland. 

How was the circulation of blood first demonstrated f What is the 
relation of lymph to blood f What effect has alcohol on the heart f 

Historical survey of the circulation. The study of the circu- 
lation was one of the first biological investigations that was con- 
ducted experimentally. In the early seventeenth century, Galileo, 
the Italian physicist, had performed and observed experiments on 
falling bodies, and William Gilbert of England had experimented 
with electric and magnetic attractions. Due to their work and in- 
fluence William Harvey (1578-1657) began to make some experi- 
mental investigation in biology. The Greek anatomist, Galen 
(131-201 a.d.), had taught that there was an ebb and flow of blood 
within both veins and arteries throughout the body. He thought 
that the left side of the heart contained blood which was vita- 
lized, by a mixture of animal spirits in the lungs. The veins were 
supposed to contain crude blood. He believed that the blood 
passed from the right to the left side of the heart through very 
minute pores in the partition. It was also supposed that one kind 
of blood flowed from the liver, to the right ventricle, to the lungs, 
and then through the veins, while another kind of blood flowed 
from the left ventricle to the lungs and then through the arteries. 
In 1510, Leonardo da Vinci wrote a manuscript which included notes 
and drawings of the heart and the blood vessels. He had studied 



the movement of the heart in living pigs and he explained how 
the aorta led from the heart and branched and ramified through 
all parts of the body. Sometime later, Vesalius attacked one of 
Galen's beliefs by doubting the existence of pores in the partition 
in the center of the heart. But people were still under the influ- 
ence of traditional teaching, and would not willingly discard too 
much of that which had been previously taught. In his dissec- 
tions, Vesalius had noted the parallel arrangement of the arteries 
and veins, but he still did not observe that the blood moved in a 
circuit. Another investigator, Cesalpino, in 1571, ventured the 
opinion that some of the blood left the heart through arteries and 
returned by, the veins. He seems to have reasoned this out with- 
out experimentation. In 1616, Harvey stated that he not only 
failed to find pores in the heart through which blood passed 
from one side to the other, but that the partition of the heart 
was unusually solid and compact. He examined the heart 
action of some forty different animals and described the pulsa- 
tions. He examined the circulatory system of a dead man 
by making an injection of warm water from the pulmonary 
artery through the lungs into the left ventricle. He finally 
concluded as a result of his observations and experimentations 
that the blood moves in a circuit, and that the beating of the 
heart supplies the propelling force. Although he understood that 
the blood moved in a " kind of circle," he did not know about the 
capillary network connecting the arteries and veins. Malpighi, in 
1660, was the first to observe, with the aid of lenses, that the blood 
moved through the capillaries from the arteries to the veins. 

Harvey's work was the result of reasoning based on the obser- 
vations of the structure and pulsations of the heart. He explained 
how the contraction of the heart forced blood into the arteries and 
how this movement produced the pulse. He pointed out that 
the amount of blood which left the left ventricle of the heart in a 
given time must return and be sent out again, because, in a half 



hour or less, the heart, by successive pulsations, forces into the 
aorta more blood than that found in the entire body. Harvey's 
discovery of the circulation of the blood opened up the field of 
physiology for later investigators. 

Source of tissue fluid. The liquid from the blood plasma is 
continuously being diffused through the walls of the blood vessels, 
into the tissue spaces where it is known as tissue fluid. This fluid 
differs from blood in that it lacks red corpuscles and may have a 
higher content of waste materials due to 
the collection of wastes from the cells. 
White corpuscles can make their way 
through the cells in the walls of the capil- 
laries and escape into the tissues; there- 
fore, they may be found in tissue fluid. 

Lymph vessels. Special vessels, similar 
to capillaries and veins, drain the excess 
fluid as it collects in the tissues, and return 
it to the blood. These are called lymph 
vessels or lymphatics and the fluid in them 
is now called lymph. The fluid that col- 
lects in a blister is lymph or tissue fluid. 
Even the smallest lymphatics are closed off 
from the tissue spaces by very thin mem- 
branes. These minute vessels lead to ves- 
sels of increasing size until they finally 
unite into two very large ones above the 
heart. The one on the left, called the 
thoracic duct, carries the lymph flow from 
the left side of the head and chest, also 
from the left arm, abdomen, and the two 
legs. The one on the right drains the lymph from the right 
side of the head and chest, and the right arm. They both lead 
into the venous system from an outlet in the superior vena cava 

Lymph vessels, known as 
lymphatics, drain the fluid 
from all the tissues of the 
body. Ultimately, they lead 
into a vein of the blood system. 



near the heart. Valves similar to those found in the veins are 

along the larger lymphatics and prevent the back flow of the lymph. 

In addition to the lymphatics that drain the tissue fluid, there are 

,%**"• ~ some called lacteals 



Liquid materials soak through the walls of capillaries and 
bathe the tissue cells. Spaces among the cells are called 
lymph spaces. The excess lymph is gathered up by special 
tubes, lymph tubes. A lymph tube is shown in the diagram 
to be parallel to a blood vessel (this representation is dia- 

that are in the villi of 
the small intestine. 
These lymphatics aid 
in the absorption of di- 
gested nutrients, par- 
ticularly fats. After 
a meal, the lacteals 
are filled with a white 
fatty substance. At 
other times, the fluid 
filling the lacteals is 
very similar to the 
lymph in the other 
lymphatics. Lymph 
is kept moving by the contraction of skeletal muscles squeezing 
the lymphatics. This is similar to the effect of the skeletal 
muscles on the veins. The flow of lymph is also controlled by the 
muscular movements of the body, and by the release of pressure 
on the thoracic duct during each inspiration. This release causes 
the lymph in vessels where the pressure is greater, to flow into the 
thoracic duct. 

The spaces formed between the membranes and the various 
organs of the body which they cover are similar in structure to 
lymphatics, and may be thought of as expanded lymph spaces. 
The fluid found in the pleural, the pericardial, and the peritoneal 
sacs is similar to the lymph in the lymphatics. 

Lymph nodes are expanded portions of the lymphatics found 
in all parts of the body. Large collections of them are located 
under the arms and in the neck. Others, in fewer numbers, occur 


in many other parts of the body. They are made of fibrous 
tissues interspersed with numerous spaces. In these spaces, white 
corpuscles collect and multiply by division. Bacteria are frequently 
brought to the lymph nodes, where they are destroyed by the pha- 
gocytes, germ-killing white corpuscles, which are found in such num- 
bers in the lymph nodes that they have little difficulty in destroy- 
ing bacteria. Occasionally, bacteria escape from the nodes and 
travel through the lymph into the blood and thus spread infections. 
If bacteria multiply rapidly and cause an infection in a lymph 
gland, a wall of calcium is sometimes deposited around the germs. 
This prevents the bacteria from escaping into the system. A 
gland of this kind can be cut out and thus the infection is re- 
moved. A lymph gland acts as a sieve to remove bacterial and 
foreign materials and thus prevents many injurious substances from 
getting into the blood and returning to the heart. The lymph 
glands of miners frequently become clogged with dirt and, there- 
fore, become greatly enlarged. 

Hygiene of the circulatory system. Blood vessels are kept in 
tone and the blood is kept circulating normally by regular exercise, 
fresh air, good food, hot and cold baths, and sufficient sleep. A large 
part of the repair of the body takes place during sleep. Many red 
corpuscles are made at this time. If one does not get enough sleep, 
pallor may result, which is due to an insufficient number of red cor- 
puscles. This may cause anaemia. Regular exercise is better than 
spasmodic exercise. When a person does not exercise sufficiently, 
the heart and arterial muscles become weak and the muscles all 
through the body lose their tone. Any unusual exercise will then 
cause palpitation of the heart. Violent emotions overstimulate the 
heart and blood vessels. Occasionally, this causes the rupture 
of a blood vessel. A violent fit of anger has been known to cause 
a condition of this kind. Drinking water is invaluable in aiding 
the blood to give off waste materials collected from the cells, into 
the organs of excretion ; namely, the lungs, skin, and kidneys. 


The cells of the body depend upon the circulatory system for 
the distribution of building and fuel materials. The importance 
of the circulatory system is, therefore, apparent. If violent physi- 
cal exercise takes place shortly after a meal, a greater supply of 
blood is sent to the working muscles and withdrawn from the di- 
gestive organs where energy is needed. Indigestion may result. 

When blood congests in veins, it causes the veins to become en- 
larged and these vessels are known as varicose veins. This con- 
dition frequently occurs in people who do not exercise or have to 
stand for long periods of time. Tight garters will retard the cir- 
culation of the blood and cause congestion. The arteries of many 
elderly people lose their elasticity. This may be caused by too 
much physical work, too much mental work, or by poor digestion. 
Calcium salts may accumulate in the walls and cause them to 
harden. This condition is known as hardening of the arteries, or 

When capillaries are broken, but the skin is unbroken, the injury 
is a bruise. Alternate hot and cold applications will usually have a 
stimulating effect. When the skin as well as the capillaries are 
broken, the injury is an abrasion. It should be washed with an 
antiseptic and bandaged to prevent infection. If arteries are cut, 
the blood flows in spurts ; pressure must be applied between the 
cut and the heart in order to prevent loss of blood. This pressure 
is best applied by means of a tourniquet which should be released 
every few minutes in order to keep the blood circulating in the limb. 
Stopping the flow of blood will help to clot the blood. If a vein 
is cut, the blood flows smoothly. In this case, the tourniquet 
should be applied on the side of the cut away from the heart. 
These are first-aid measures only, and in case of an injury to a vein 
or artery of considerable size, a physician should be called to treat 
the cut. 

Alcohol is believed to injure the white corpuscles to such an ex- 
tent that they lose their ability to destroy germs. It also dilates 


blood vessels, causing them to lose their ability of contracting and 
relaxing. Tobacco is likely to cause palpitation of the heart. 
Both alcohol and tobacco seemingly interfere with good physique. 
For that reason, part of an athlete's training is abstinence from 
them. Good health habits exclude alcohol, tobacco, and drugs. 

Questions and Suggestions 

1. How was it possible for early scientists to study the circulatory 
system scientifically ? 

2. What three erroneous ideas in regard to circulation were ex- 
ploded through the scientific method ? 

3. Draw a diagram of a liver cell, a lymphatic, and a capillary. By 
means of labeled arrows, indicate the possible exchanges of materials. 

4. In what cells in the body can blood leave an unusual supply of 
(a) calcium, (6) fat, (c) worn-out red corpuscles, (d) protein for destruc- 
tion ? Where can it collect (a) oxygen, (6) urea, (c) white corpuscles, 
(d) glucose? 

5. What is the relation of the lymph system to the blood system ? 

6. What rules of health should be followed if the organs of circu- 
lation are to be kept in the best possible condition ? 

7. In terms of circulation, discuss a possible cause of each of the 
following diseases : anaemia, varicose veins, and hardening of the 

Supplementary Readings 

Haggard, H. W., The Science of Health and Disease (Harper & Bros.). 
Kimber, D. C, and Gray, C. E. Textbook of Anatomy and Physiology (The 
Macmillan Co.). 

WH. FITZ. AD. BIO. — 12 

1 *• • . y 

• '.i 

(6 !St 




Excretory organ of Parame- 

Excretory organ of earth- 

What is the necessity for excretion f How are wastes eliminated from 
the body f What is the relation of the skin and kidneys to excretion f 

Importance of excretion. The wastes formed in the various 
tissues as a result of oxidation are carbon dioxide, water, organic 
salts, and urea (nitrogenous compound) . These wastes would in- 
terfere with the normal functions of the cells unless removed as 
quickly as formed. The removal of these wastes is called excre- 
tion, and the organs that eliminate the wastes are called the excre- 
tory organs. The importance of an efficient system of elimination 
can not be sufficiently emphasized. Carbon dioxide is eliminated 
chiefly by the lungs, although some is dissolved in water and 
is excreted by the skin and kidneys. Water and some soluble 
salts are eliminated by the skin as perspiration, and by the kid- 
neys as urine. Some water, however, passes out of the lungs in 
the form of vapor. Most of the urea is excreted through the 
kidneys as part of the urine, and a small amount through the skin 
x as part of the perspiration. 

Problem. Study of the skin. 

I. Touch the skin and describe how it feels. 

A. Explain the source of the heat in the skin. 

B. When one is exercising violently, why does the skin become much 
warmer than it does at other times ? 



II. Describe the skin of the hand as it appears to the eye. Tiny structures 
in the deeper layers of the skin push up the outer layer into little ridges. 

A. Note the arrangement of the lines on the tips of the fingers, particu- 
larly the thumb. Describe the arrangement. 

B. Moisten the finger slightly and, if convenient, touch powdered car- 
bon with it. Then press it on clean blank paper. 

1. What is the impression called? 

2. What use may finger prints serve ? 

C. Examine your skin and observe whether it normally has breaks or 
abrasions on it. What is the value of an unbroken skin ? 

III. Hold the hand out straight and then clinch the fist. Does the skin 
appear dry and brittle or soft and flexible ? 

A. This characteristic is due to oil secreted in oil glands in the skin.- 

B. Describe what may have happened to cause dry skin. 

'IV. Touch your tongue to the back of your hand. Describe the taste. 
This is due to perspiration secreted by sweat glands in the skin. 

A. Why is the perspiration not always seen on the skin? 

B. What condition favors the evaporation of the perspiration ? 

C. What condition hinders the evaporation of the perspiration ? 

D. Under what conditions do we perspire excessively ? Why ? 

V. If wet-and-dry-bulb thermometers are available, pour a little water on 
the bulb. 

A. After a few minutes, read and record the temperature of each 

B. What effect has the evaporation of moisture on temperature? 

C. What effect would you expect the evaporation of perspiration to 
have on the temperature of the body ? 

VI. Hold the hand so that the back of it is on a level with the eyes. Note 
the hairs covering it. These hairs probably help to absorb perspiration from 
the skin. 

VII. Cite some evidences of the skin gradually peeling from your body. 
This is the outer dead skin called the epidermis. 

VIII. Prick the skin gently with a pin. As a result of the pin prick tell : 

A. What two sensations may be experienced by the nerve endings in 
the skin. 

B. What other sensation may be experienced by skin ? 

IX. Summarize your answers to the above questions by stating four 
functions of skin. 



por« ofsvteat ^lan^t'&uer^ 


Structure of the skin. The skin is a smooth, moist, flexible 
organ varying from one one hundredth to' one tenth of an inch in 

thickness. It consists 
of an outer layer called 
the epidermis, and an 
inner layer called the 
dermis. As the cells 
grow out in the deep- 
est part of the epider- 
mis layer, they are 
gradually transformed 
into flat scales. The 
outermost layers are 
dead and are being 
constantly rubbed off 
the surface of the skin. 
The deepest layer of 
the epidermis contains 
pigment cells, and is 
called the Malpighian 
layer after the scien- 
tist who first observed 
it. There are normal pigments in this layer, which are the basis 
for white, yellow, red, or black skin colors of various people. In this 
layer may develop deposits of pigment, which are known as freckles. 
The dermis is the true skin. It is composed largely of connec- 
tive tissue. Tiny muscles may run through the dermis. These, 
by contracting, will cause the tiny hairs in the epidermis to stand 
erect. They also cause the " goose flesh " when a person is cold. 
The contraction of millions of tiny muscles give a little heat and, 
at the same time, a warning that the body is cold. . The dermis is 
richly supplied with blood vessels, lymph vessels, nerves, and hair 
follicles. The blood vessels carry water in which urea and carbon 


The surface cells of the skin are constantly wearing or 
washing off and are replaced by cells underneath. Blood 
vessels nourish the skin; and the various nerve endings re- 
ceive different stimuli from the environment. 



dioxide are dissolved. Some of the wastes are eliminated by 
sweat glands. Each sweat gland ends in an opening in the epi- 
dermis called a pore. The perspiration leaves the body through 
the pores. . Specialized epithelial cells form roots of hairs in the 
deeper layers of the true skin. These hairs grow out through 
hair follicles which are formed by the downward extension of the 
epidermis. Only the lower part of the hair lives and grows. 
Associated with the hair follicle is an oil gland. This supplies 
nourishment to the hair since it opens either into a hair follicle 
or upon the surface of the skin. The oil keeps the skin flexible 
and soft. Within the tiny papillae or end-organs in the dermis 
are specialized nerves for receiving the sensations of pressure, 
pain, and temperature. Fat cells are also found in the dermis. 

Functions of the skin. The skin is an organ of excretion. By 
means of the millions of blood vessels, sweat glands, and pores, it 

Hairs grow from hair follicles formed by 
the downward extension of the epidermis 
into the true skin. The hair in the bottom of 
the follicle enlarges to form a bulb which is 
well supplied with blood vessels. 

<K>W..J ■■■ 

A sweat gland is composed of a duct and 
a coiled portion surrounded by capillaries. 
Wastes gathered from the blood by the 
glands are eliminated through a pore in the 




The ski a is an organ of feeling. The 
papillae put us in touch with our environ- 
ment by sensing pressure, pain, and tem- 

excretes on an average of a quart of perspiration daily. In cases 
of kidney trouble, it may relieve the kidneys by secreting more 
wastes. The skin is an organ of protection. By means of its un- 
broken outer dead layer of epi- 
dermis, it protects the underlying 
living dermis from an excessive 
loss of water and from the in- 
vasion of germs and dirt. The 
skin is an organ of sensation. 
By means of the papillae in the 
dermis, it receives sensations of 
pressure, pain, and temperature. 
The skin is invaluable in equaliz- 
ing and maintaining the proper 
body temperature. If the body is too warm, a greater supply of 
blood is sent to the skin so that the heat will radiate. If the body 
is not sufficiently warm, the blood vessels in the skin contract and 
very little heat radiates out. The evaporation of the perspira- 
tion on the skin cools the body. 

Hygiene of the skin. When the water of the perspiration evap- 
orates, organic salts and urea clog the pores. These wastes can best 
be removed by warm, soapy baths. If left in 
the pores, the wastes, resulting from perspira- 
tion, give the body an objectionable odor. A 
tepid bath should be taken at least twice a 
week. Cold showers are stimulating to the skin, 
muscles, and the blood vessels, and, if possible, 
should be taken daily. Dirt may clog the 
pores in the skin and cause blackheads. If the 
skin is kept clean, blackheads will not form. 
Sometimes bacteria clog the pores, and cause infections, pimples, 
or possibly boils. Pimples should not be pinched or scratched 
with the fingers as bruises may result and cause more serious 


Papillae on the tongue 
contain nerve endings 
which transmit taste 
stimuli to the brain. 



infections. Let them heal naturally or have a physician care 
for them. When pimples become chronic, the condition is 
called acne. If acne is 

vena cava 



The kidneys gather liquid wastes from the blood. 
These materials are passed through the ureters to the 
bladder and held in this reservoir ready for excretion. 

treated in time, it can 
be cleared up completely. 
If not, it leaves scars 
that are permanent. 
Any unhygienic condition 
of the body is likely to 
affect the skin. In order 
to keep the skin in good 
condition, hygienic sug- 
gestions concerning food, 
water, rest, exercise, and 
sunlight should be fol- 

The kidneys. The or- 
gans that excrete most of 
the water and urea from the body are the kidneys. They lie in 
the abdominal cavity in the small of the back above the waist 
line. They are bean-shaped with the concave side turned toward 
the spine. The bulk of the kidney is made up of small coiled 

tubes, tubules, closely packed 
together and containing a large 
number of blood vessels, and 
some nerves and lymphatics. 
Water, urea, and organic salts 
pass by means of osmosis into 
the tubules. These tubules 
lead into two tubes, one 
from either kidney, the ureters, which are connected to a hollow 
muscular sac called the bladder. The kidneys secrete urine which 
passes down the ureters to the bladder. The bladder serves as a 


ttfbule of 

The kidneys are made up of numerous minute 
tubules. Their intimate relation with blood ves- 
sels makes possible the absorption of wastes. 


reservoir for the urine until it is expelled from the body. When 
the bladder is moderately distended, it holds about one pint. The 
average quantity of urine secreted in twenty-four hours by the 
average adult is about forty ounces, or 1.2 liters. The kidneys 
eliminate toxic materials formed in the body during illness. In 
ridding the body of its poisons, the kidneys are frequently dam- 
aged. In order to keep them in as good condition as possible, 
about seven glasses of water should be drunk daily. This will 
dilute any toxic materials present and keep the kidneys well 
washed. Too much animal protein food should not be eaten as 
the kidneys may become overworked, in eliminating the urea, an 
oxidation product of proteins. 

Questions and Suggestions 

1. What is excretion? 

2. Name the organs of excretion and discuss how each one elimi- 
nates waste. 

3. Name four functions of the skin and explain the ways in which 
the skin is adapted to perform each function. 

4. Discuss the hygiene of the skin. 

5. What unhygienic habits may injure the skin ? 

6. What is the relation of the work of the skin to the work of the 
kidneys ? 

7. Discuss the value of water to the skin and kidneys. 

Supplementary Reading 

Kimber, D. C, and Gray, C. E., Textbook. of Anatomy and Physiology (The 
Macmillan Co.). 


Tracheae of insects. 

Gills of fish. 

What is the relation of respiration to excretion f 
perform their function? 

How do the lungs 

Most of the carbon dioxide and some of the water, formed by 
the body cells during the oxidation of food materials, are eliminated 
through the lungs. There are no organs in a higher plant similar 
to the lungs of man, although the stomata, openings for the in- 
take and outgo of air, in leaves are concerned with the function 
of respiration in the plants. The abundance of these stomata 
make up for their microscopic size. ,They are found in the epi- 
dermal tissues of a leaf and they lead to air spaces among cells 
between the two layers of epidermis. These openings are not 
adapted for securing large quantities of air at one time. They 
may be compared to the nostrils of man rather than to the lungs. 

Lower animals have various devices for securing air. An insect 
has small openings in the abdomen and thorax which lead into 
branching tubes. These tubes subdivide until they can reach the 
smallest cell in the body. By compressing and releasing their 
body regions, somewhat like a bellows, the animals are able to 
take in oxygen and give out carbon dioxide. Watch the abdomen 
of a fly or a bee and note the breathing movements. A fish has 
gills which are branched structures with such thin walls that air 
can pass directly from the water into the blood stream. The air 




is taken from the water which is drawn into the mouth and forced 
out through the gills. Respiration takes place in every living cell, 
but breathing is only possible in the higher animals that have lungs. 
The air tubes. The outer openings of the air tubes of man are 
the nostrils. These lead into two nasal passages terminating in the 
throat cavity. The nasal passages are specially adapted for pre- 


The breathing organs of man are arranged in a continuous passageway from the nostrils 
to the ends of the bronchial tubes. These tubes subdivide and terminate in air sacs. 

paring air for the use of the body. The hairs in the nose act as a 
filter, to keep dust and other foreign particles from entering the 
lungs. The mucous lining absorbs the fine foreign particles and 
inhibits the development of germs. The mucous lining also 
moistens the air. Very dry air is irritating to the lungs. 

The air is warmed in the nasal passages by coming in contact 
with the blood vessels in the linings of the narrow passageways. 
Air then passes through the glottis into the larynx or voice box. 


The larynx contains some thickened cartilage, popularly called 
Adam's apple, which projects slightly on the front of the neck. The 
air passes down the trachea or windpipe into the two branches, 
the bronchi, which subdivide again and again into the bronchial 
tubes, which in turn end in small pouchlike sacs called the air 
sacs. All of the air tubes are lined with mucous membrane 
vvhich warms and moistens the air. The trachea is lined with 
specialized epithelial cells bearing hairlike processes or cilia. These 
cilia are in constant motion. Their function is to push or move any 
solid particles, in the air, into the throat, where they are expelled. 

There are numerous capillaries in the air sacs. The walls of 
the capillaries are membranous and air easily diffuses through 
them into the blood. The red corpuscles take the oxygen from 
the air. Thus blood becomes oxygenated. At the same time, the 
blood gives out its carbon dioxide. The air sacs may be com- 
pared with tiny balloons. The fact that they are so numerous and 
are capable of such inflation affords a tremendous surface for the 
absorption of oxygen even though the lungs themselves are fairly 
small. The large absorbing surface of the air sacs makes possible 
the presence of a tremendous number of capillaries running through 
them. Therefore, a great deal of oxygen quickly passes into the 
blood and carbon dioxide passes out. The lungs consist of mil- 
lions of air sacs and bronchial tubes held together by connective 
tissue. The moist membranous pleurae cover the lungs, and pre- 
vent friction during the breathing movements. 

Diseases of the respiratory tract. The mucous membrane 
lining the pharynx contains many lymph glands and at the back 
and upper part of the cavity there is a large mass of this lym- 
phoid tissue. During infancy and childhood this tissue may 
increase greatly, and the child is then said to have adenoids. 
Adenoids are a menace to health. They may obstruct the openings 
to the Eustachian tubes, and in some cases cause deafness. - They 
usually interfere with the passage of air through the nose and 




necessitate mouth breathing. This not only allows dust and other 
foreign particles to pass into the lungs, but tends to alter the shape 
of the jaws and facial features. Malformations of teeth are fre- 
quently caused by adenoids. 
Mouth breathing is usually 
a forced breathing and 
frequently alters the shape 
of the chest. 

In the lower part of the 

Thickened mucous membranes may form abnormal throat, On either side, are 

growths, known as adenoids, in the back of the nasal .. » , l • j 

passageways. Tonsils are the normal growth of lym- Small masses 01 lymphoid 

phoid tissue in the throat. ,. „ i /nW/» The 

LlooUC CdllCLl LUILol/Vo. .JLJlv 

function of the tonsils is not understood exactly. They are 
thought, when in a normal condition, to help protect the body 
from infection by acting as filters and preventing the entrance 
of bacteria. If they become infected with bacterial growths, they 
serve only as centers of infection. When they are infected, the 
pus in them passes directly into the lymph and then into the blood. 
This may cause such conditions as rheumatism, anaemia, or pro- 
duce an undesirable heart condition. If the tonsils become much 
enlarged, they fill the throat cavity and interfere with the passage 
of air to the lungs and of food to the gullet. Inflammation of the 
tonsils is called tonsillitis. 

Problem. Study of the lungs. 

Secure the lungs and windpipe of a sheep or lamb from the butcher. 

I. Try to cut the windpipe or trachea. 

A. Describe the structure. 

B. What is the value of the presence of cartilage in the trachea? 

C. Describe the arrangement of the cartilage in the trachea. 

II. Observe the appearance of the lungs. 

A. Describe the outer shiny covering. Discuss the functions of the 

B. Describe the structure of the lungs, including the shape, texture, 
color, and tissues present. 


C. Insert a glass tube in the trachea and breathe into it. 

1. What effect has this on the lungs? 

2. When you blow into the lungs, do you find any structuresjthat 
might account for the texture of the lungs ? 

III. Cut out a small piece of the lung tissue where the bronchus enters it. 

A. Describe the branches of the bronchus in the lungs. 

B. Try to trace one of the tubes until it ends. How does it end ? 

Problem. Study of the mechanics of breathing. 

Place a cork, through which runs a glass rod, in the mouth of a small-sized 
bell jar. Attach a balloon to the end of the rod inside the jar. Cover the 
bottom of the jar with a piece of rubber sheeting in the center of which a string 
is attached. 

I. To what structures in our bodies are the glass tube, balloon, bell 
jar, and rubber sheeting comparable ? 

II. Pull the string gently, so that the rubber sheeting moves down. 

A. What effect has the lowering of the rubber sheeting on the balloon ? 

B. Is the balloon pressed on by air in this position of the rubber sheet- 
ing as much as in the former position ? 

C. When the pressure on the outside of the balloon is released, what 
effect has it on the air in the balloon ? 

D. Why, then, does air enter the balloon ? 

E. To what is this comparable in human breathing ? 

III. Push the rubber sheeting into the battery jar to form an arch. 

A. What effect has the arching of the rubber sheeting on the balloon ? 

B. In this position, is the balloon pressed on by air as much as in the 
lowered position ? 

C. When the pressure on the outside of the balloon is increased, what 
effect has it on the air in the balloon ? 

D. Why, then, does air go out of the balloon ? 

E. To what is this comparable in human breathing ? 

IV. To what is the inflation and deflation of air in the balloon due ? 

V. What is one of the reasons for inspiration and expiration in man ? 

Mechanism of breathing. Air with its oxygen is taken in, and 
air with increased amounts of carbon dioxide is given off as a re- 
sult of muscular activity. The floor of the chest cavity is formed 
by the muscular diaphragm. The upper surface of the diaphragm 


is arched around the lower part of the heart and lungs. When 
its muscular portion contracts, the diaphragm flattens and moves 
downward, while the ribs are elevated. The spaces between the 
ribs are filled by muscles. When these muscles relax the ribs 
return to their original position. This reduces the chest cavity 
from side to side. The diaphragm now returns to its original 
position and the abdominal walls contract and push the liver and 
stomach against the diaphragm, which contracts, presses against 
the lungs, and in so doing, pushes out the walls of the chest 
cavity, front and back. Thus the chest cavity is increased in size 
from top to bottom by the contraction of the diaphragm, and 
from back to front and side to side by the activity of the muscles 
between the ribs. 

The lungs are as large as the cavity they occupy. When the 
chest cavity increases in size, the lungs are no longer pressed 
upon, and, since they are somewhat elastic, they fill the space 
made by the expanding chest. The air in the lungs now spreads 
out to fill the space formed by the enlarging of the lungs. Move- 
ment of air always occurs when there are differences in pressure. 
As the air spreads out, its density becomes lower. Air rushes in 
from the outside to equalize the pressure. This is inspiration or 
the taking in of air. The blood vessels in the air sacs are thus sup- 
plied with air from which the haemoglobin extracts oxygen and 
to which it gives up carbon dioxide. 

Expiration is the forcing out of air. It is due to the relaxation 
of muscles which crowd the lungs into a smaller space. Air in the 
lungs is then denser than air outside and it is expelled in order to 
equalize the pressure. This is expiration. The taking in of the 
air, the exchange of gases in the air sacs, and the giving out of air 
is breathing or respiration. 

Cell respiration.* When the oxygen of the air gets into the blood, 
it is carried to the cells. It passes from the blood through the 
walls of the capillaries, through the lymph spaces and into the cells. 


Oxidation of the food then takes place, releasing energy for cell 
work and forming the wastes, carbon dioxide, water, and urea. 
The carbon dioxide is given off to the blood. Respiration is of 
two types, external respiration and internal respiration. External 
respiration is concerned with inspiration and expiration. Internal 
respiration involves the exchange of air between the blood and 

The rate of respiration. The average rate of respiration for an 
adult is twelve to sixteen per minute. This rate is partly deter- 
mined by the amount of carbon dioxide in blood. If this amount 
rises above a certain percentage, the nerve centers controlling res- 
piration are stimulated and this results in deeper breathing at an 
increased rate. Thus more oxygen is obtained and the carbon 
dioxide is removed more rapidly. This explains the second wind 
of athletes. Due to violent exercise, a great deal of oxidation 
takes place, causing the accumulation of carbon dioxide in the 
blood. Then the nervous response follows, increasing the respira- 
tory rate and giving the athlete more oxygen for releasing more 
energy. The rate of respiration may, also, be influenced by strong 
emotion and by old age. In respiration, the lungs are never 
emptied of air; only about one tenth of the air is normally 
changed with each respiratory movement. This is called tidal air. 

Problem. Modifications of breathing. 

I. Analyze the type of respiration, and next to each write whether it is 
an inspiration or an expiration in each of the following : yawning, sighing, 
sneezing, coughing, hiccuping, sobbing. 

II. Explain how the control of the diaphragm will probably suppress any 
one of them. 

The air we breathe. Inspired air contains about 20.96 per cent 
oxygen, 79 per cent nitrogen, and 0.04 per cent carbon dioxide: 
Expired air contains about 16.4 per cent oxygen, 79 per cent ni- 
trogen, and 4.1 per cent carbon dioxide. The same air can be 
breathed many times before the oxygen is entirely exhausted. 



Through experimentation, scientists have discovered that people 
are most uncomfortable in still air. Under the clothing, in close 
contact with the skin, is a blanket of air. This air absorbs per- 
spiration, body odors, and the excess body heat. If this air can- 
not circulate, it becomes moist, and the perspiration does not 
evaporate as it should. If air in a room is set in motion by an 
electric fan, the contaminated and moist air moves, and cooler 
and drier air takes its place. This brings relief to the body. For 
years, people thought ventilation consisted largely of getting rid 

from, Tieart 
to tissue cells 

Ctno.u* Sac 
of -tftc. lung 

incoming ovr tdiili ojp*£«^ 
ou*co*ntW*o«V* owWLIess 

The exchange of carbon dioxide and oxygen between the air sacs and blood vessels is external 
respiration ; between the cells and blood vessels it is known as internal respiration. 

of carbon dioxide. Now it is known that ventilation problems 
also involve the control of body odors, heat, and moisture. 

When air is set in motion, the stagnant air is removed and 
fresh air is brought in contact with the body. Air that is best 
for breathing should be at a temperature from about 65 degrees 
to 70 degrees. It. must be slightly moist, must be moving, and 
must be free from dust and impurities. The problem of venti- 
lation is to treat the atmosphere of a room so that air will have 
at all times the four characteristics mentioned. 


Methods of ventilation. Many systems of ventilation have been 
devised, but probably in many places none works as efficiently as 
properly regulated windows. Windows should be opened at the 
top and bottom during both day and night. Air comes in the 
lower opening, becomes heated, rises, and goes out through the 
upper openings. Care should be taken that drafts are kept out 
of the room since these are likely to chill the body. A board 
placed at the bottom of an open window can be arranged so as to 
drive the air upward and will thus prevent drafts. In winter, 
care must be taken to keep the air moist. If the air is too dry, 
the mucous membrane lining of the nose and throat will become 
dry and irritated, probably resulting in inflammation in the res- 
piratory tract. The various methods of heating homes are likely 
to dry the air. The evaporation of water in pans placed under 
or on radiators will aid greatly in moistening the air. To-day, 
we find that ventilating systems are included in many of the 
modern heating plants. In these systems the same air is circu- 
lated repeatedly. It is washed, heated or cooled, and freed of 
moisture in each circuit. 

Hygiene of respiration. A great many deaths are caused an- 
nually by diseases of the respiratory tract. Many of these could 
be prevented if the respiratory tract were kept in good condition. 
The nose is adapted for preparing the air for the use of the 
body, and, therefore, it should be used for breathing. Any inter- 
ference with nasal breathing should be corrected. 

Questions and Suggestions 

1. Suggest two experiments that may be used to show that oxida- 
tion takes place in the body. 

2. Name the adaptations of the respiratory system for (a) puri- 
fying air, (6) warming air, (c) moistening air. 

3. Make a labeled diagram of the air passages. Trace the path 
of air from the time it first enters the body until it reaches the 

WH. FITZ. AD. BIO. — 13 


4. Discuss the mechanics of breathing. 

5. State the aims of ventilation. 

6. How would you ventilate a room ? 

7. What causes discomfort in a poorly ventilated room ? 

8. In a diagram containing a cell, lymph space, and a capillary 
indicate, by means of arrows, how respiration takes place. 

9. Build a box to illustrate a room with two windows. Manipu- 
late the windows to illustrate proper ventilation. Candles may be 
used to show the best methods of ventilation. 

Supplementary Readings 

Howell,. W. H., Textbook of Physiology (W. B. Saunders Co.). 
Williams, S. F., Healthful Living (The Macmillan Co.). 


Exercise promotes 

good metabolism. 

What is metabolism? How are the food nutrients used in the body? 

Metabolism is the term usually applied to all the processes which 
are concerned in the building up and breaking down of the proto- 
plasm in an organism. In short, it is the sum total of all the physi- 
cal and chemical changes by which the protoplasm utilizes food, 
releases .energy, and eliminates waste products in order to maintain, 
repair, and produce more protoplasm. The processes of absorp- 
tion, assimilation, respiration, and excretion are phases of metab- 
olism, while digestion may be called a secondary process which 
makes possible the primary activity of absorption. If the process 
of metabolism is that of synthesis or building up, it is called an- 
abolism, but if the process is one of tearing down, it is katabolism. 
When the building up of protoplasm is greater than the breaking 
down, growth takes place. 

No one function of the body can be discussed without referring 
to one or all of the others because many of the functions take place 
at the same time. During the anabolic process of assimilation, the 
katabolic process of oxidation is also being carried on in order to 
release enough energy for the assimilation and growth processes. 
Before oxidation is possible, the digestion of the food must take 
place. In fact, the process of metabolism involves all the physi- 
ological functions of the body as well as the special activities that 




take place within the cells themselves. No matter what kind 
of food is taken into the body, it must first be broken down 
into a soluble form, and assimilated by the cell, before it can 
be converted into the kind of tissue needed. 

Metabolism of carbohydrates. All carbohydrates are reduced 
to simple sugars, glucose or galactose, in the digestive process, 
by means of enzymes. They are then absorbed by the capillaries 
in the villi and sent to the liver by way of the portal vein. The 
excess sugar is taken in by the liver and stored there as an in- 
soluble form of carbohydrate, known as glycogen or animal starch. 
Muscle cells, too, store up small quantities of sugars in the form 
of glycogen. This glycogen is then con- 
verted, as it is needed, into glucose and 
given to the blood. Thus the percentage 
of sugar in the blood is kept constant at 
0.07 to 0.15 per cent. If more carbohy- 
drates are eaten than can be used or stored, 
the surplus tends to be converted into body 
fat. As the sugar circulates, it is absorbed 
in the tissue fluid and cells by means of 
osmosis. Here it is oxidized to release 
energy in the form of muscular work or heat 
to keep the temperature of the body con- 
stant. In the oxidation process, sugar is 
converted into carbon dioxide and water. 
These wastes are carried by the blood to 
the lungs, skin, and kidneys for elimination 
from the body. 

Metabolism of protein. Proteins are de- 
composed by enzymes in the digestive tract 
into the simple compounds, amino-acids. 
These are absorbed into the blood and from there into the tissue 
iluid and cells. The body uses the various amino-acids for build- 

The food burned in a bomb 
calorimeter and the energy 
released is carefully deter- 
mined. The number of cal- 
ories shown in the food tables 
is found in this manner. 



Underwood and Underwood 
The amounts of human energy expended in various types of work can be measured by a calor- 
imeter. This is done by devices which measure the amount of oxygen absorbed and the amount 
of carbon dioxide given off by the subject doing a particular kind of work. 

ing new cells and for repairing any wastage. If there is a surplus 
of protein materials it is thought that a portion is held as a sort 
of storage supply in the liquids or tissues of the body. This sur- 
plus is then utilized when the loss of protein from the cell is 
greater than the supply needed by the body for repair, as in time 
of illness. 

If there are more proteins (in the form of amino-acids) than 
the cells can utilize, some of the excess is eliminated by the 
kidneys, while others are taken care of by cells in the liver. 
These cells in the liver are capable of separating the amino-acids 
into ammonia and non-nitrogenous products (oxygen, hydrogen, 
carbon, sulphur, and phosphorus). The ammonia combines with 
other elements to form urea which is eliminated by the kidneys as 


fast as it is formed. The sulphur and phosphorus are given off by 
the excretory organs, and the carbon, hydrogen, and oxygen com- 
bine and are stored in the liver in the form of glycogen. This sub- 
stance is then released as the body needs it. 

Metabolism of fats. Fats are absorbed as glycerol, fatty acids, 
and soaps by the lacteals of the villi. In the absorption process, 
they are reassembled as fats, probably by the epithelial cells in the 
villi. The absorbed fats travel through the lymphatics to the 
thoracic duct which empties them into the venous system just before 
draining into the superior vena cava. In this way, they become a 
part of the blood. These fats are not in the original form of the 
fat ; they are made into a fat which is characteristic of the species 
in which the metabolism is taking place. They are carried to the 
cells, where they are burned as fuel which serves as a source of 
energy for muscular work and other activities. The resulting 
wastes, carbon dioxide and water, are eliminated by the organs of 
excretion. Some fat is used to build fatty tissue and the extra fat 
is then stored in the vacuoles of cells in the form of drops of oil. 


1. Give a definition of metabolism. 

2. Classify the functions of the body into anabolic and katabolic 

3. Discuss the metabolism of sugar ; of protein ; of fat. 

Supplementary Readings 

Burton-Opitz, Textbook of Physiology (W. B. Saunders Co.). 
Howell, W. H., Textbook of Physiology (W. B. Saunders Co.). 
Martin and Weymouth, Elements of Physiology (Lea & Febiger). 
Mitchell, P. H., General Physiology (McGraw-Hill Book Co.). 

^Z_voice base 






The. thyroid gland. 

An adrenal gland. 

' What are ductless glands t How do they affect the development and the 
activity of the body? What is the scientific status of gland grafting? 

The glands of the body, that have already been discussed, had 
ducts to convey their secretions to an outer surface, such as the 
mouth, stomach, or skin. Certain glands in the body have no 
ducts, but pass their secretions directly into the blood or lymph. 
These glands are called endocrine glands (endocrine is from a Greek 
word which means " to separate within ") . These glands manu- 
facture substances which go into the blood stream, and activate 
or influence another organ or organs in the body. These manu- 
factured substances are called hormones (from the Greek word 
meaning to " excite " or " arouse "). 

Internal secretions. The hormone secretin was mentioned 
when the digestive system was studied. It is liberated from the 
wall of the small intestine when the acid food enters from the 
stomach. It is absorbed directly into the blood and is carried to 
the pancreas and liver. It stimulates these glands to activity so 
that the bile and pancreatic juice immediately start to flow. 
Carefully checked experiments have proven that this activity 
always takes place. For example, an experiment was given in 
the chapter on digestion to show that secretin travels through 
the blood from the intestine to the pancreas. Another interest- 
ing experiment has been performed to show how digestive juices 




are produced. Some of the mucous membrane of the small in- 
testine was scraped off, treated with acid, and injected into the 
~ , blood. Immediately, pan- 

creatic juice flowed. The 
flow is thought to have 
been effected by the stim- 
ulation of the digestive 
glands by secretin which 
was probably formed from 
an inactive hormone in the 
mucous membrane. 

The internal secretions 
are of great importance in 
bringing about coordina- 
tion among the various 
organs. It is thought by 
some investigators that 
every kind of tissue may 
give rise to individual sub- 
stances or principles which pass directly into the blood, and affect 
the general working or metabolism of the body. Not many studies 
have been published concerning tissue secretion. To date, in- 
vestigations have been confined largely to the hormones of the 
ductless glands. 

It is difficult to secure the internal glandular secretions of human 
beings in a pure state. Therefore, our knowledge concerning 
them is based primarily on experimentation >on lower animals, 
chemical examination of the glands and their extracts, and of 
the blood near the glands, observations of the effects resulting 
from disturbances of the ductless glands, and effect of direct 
injections of extracted or synthesized internal secretions. 

The thyroid. The thyroid is one of the ductless glands. It is 
situated in the neck and consists of two divisions or lobes, one on 

pineal bo&£ 




Most of the ductless glands of man are indicated in 
their approximate positions. 



either side of the voice box or larynx, and usually connected by a 
narrow strip of tissue. The entire structure weighs between one 
and two ounces. The substance secreted by the thyroid is called 
thyroxin and it contains about 65 per cent of iodine. It passes 
directly into the blood since there is no duct to convey it from the 
gland. Thyroxin influences the rate of oxidation in the body. 
The method of testing this rate is by determining the person's basal 
metabolism. Basal metabolism means the heat or energy expended 
by the body when there is almost complete absence of absorption 
from the digestive tract, and almost complete muscular and mental 
repose. A normal person who has fasted for fifteen hours preced- 
ing the test would use a definite amount of oxygen, depending on 
his weight, height, and age. This amount has been determined, 
and is a measure of normal basal metabolism. Doctors can tell 
whether or not a thyroid gland in any person is overactive by 
performing this basal metabolism test. A large amount of thyroid 
secretion increases the metabolism in the body, which is noted by 
an increase in the amount of oxygen used, as compared with the 
amount used by a normal person. A decrease in thyroid secre- 
tion results in a lower rate of basal metabolism; that is, less 
oxygen is used than that usually required by a normal person. 

I Brain... 
t"hyroicL _> V y / 

pineal £lcttul 


The location of the ductless glands in the rat. 

Thyroids have been removed from animals, and harmful effects 
were observed. Other thyroids were grafted in another section 


of the body, and the aforementioned results disappeared, although 
the effect of the grafted thyroids were only temporary. Extracts 
of the thyroid tissue are now given to persons whose glands do 
not function properly. In most cases the treatment is successful. 

Thyroxin probably has some effect upon growth and develop- 
ment of organisms. Gudernatch, while teaching at Columbia 
University, has carried on a series of interesting experiments on 
glandular feeding. He fed thyroid glands (of different animals) 
to very young tadpoles and they promptly went through meta- 
morphosis and became frogs. In some cases the frogs were no 
larger than a beetle. When he removed the thyroid gland from 
other tadpoles, they never became frogs, although they grew larger 
than the usual size of a tadpole. 

Thyroid deficiency, due to degeneration or an operative removal 
of the glands, in an adult gives rise to dullness and general 
apathy or sluggishness. The person gets very stout, although his 
appetite may be diminished. The heart beats slower, the nervous 
system becomes sluggish, and the general intelligence is lowered. 
This condition is easily explained by the slow rate of oxidation. 
The disease is called myxedema. If in a young child the thyroid 
glands waste away, his head and face usually become enlarged, and 
look deformed, and his abdomen becomes swollen. The mental 
faculties as well as the physical character of these sufferers show 
lack of development and often lead to a condition of idiocy. This 
disease is called cretinism, and children suffering from it are called 
cretins. When thyroid extract is fed to persons suffering from 
myxedema or cretinism, they usually improve and sometimes are 
completely cured, provided no essential organs have been affected. 
This thyroid treatment must, however, be kept up indefinitely 
because the patients' glands are atrophied and will remain inactive.^ 

In some communities, a large percentage of the population shows 
an enlargement of the thyroid glands ; -this condition is known as 
endemic goiter. It is common in certain sections of our country. 


One might think that the thyroid is over active in endemic goiter, 
since it is enlarged. However, the reverse is true as the general 
symptoms are the same as in myxedema. Thyroid tissue is rich in 
iodine. This is a constituent always present in drinking water 
of localities near the sea, in sea weed, and in sea foods 'such as 
oysters and crabs. When people live in areas remote from the 
sea, they drink glacial water which is practically lacking in iodine. 
Endemic goiter is usually prevalent in such districts. An example 
is our own Great Lake district. Studies have been made in many 
schools in these localities. Inorganic iodides have been admin- 
istered to the children and iodine has been put in their drinking 
water. Within a short time the number of cases of goiter showed 
a remarkable decrease. However, it is probably unwise to feed 
iodine as a treatment to all people suffering from endemic goiter. 
In case the gland is already enlarged, the iodine, may stimulate 
the gland to produce too much thyroxin. This would increase 
the metabolism of the body. When people suffer from excessive 
thyroid activity, foods containing iodine are often removed from 
their diets. In all cases iodine should be used only upon the 
advice of a physician. 

An excessive secretion of thyroxin gives rise to a disease called 
exophthalmic goiter. The symptoms'are just the opposite of those 
in underactivity of the gland. Instead of a stupid, apathetic con- 
dition there is a restless, nervous one. There is a wasting away of 
tissues in spite of an enormous increase in food consumption. The 
pulse and heart action are very rapid and often irregular. The 
thyroid usually increases in size accompanied by an abnormal 
protrusion of the eyeballs. There are various treatments, the most 
successful being complete rest in order to slow up metabolism. 
Sometimes, X-rays are used to check the activity of secretion and 
sometimes the gland is partially removed. A more common 
operation is the tying off, temporarily, of one of the blood vessels 
in order to lessen the amount of the secretion reaching the blood* 



The parathyroid. There are four small structures attached to 
the thyroid glands, and weighing in all about two grains. They are 
the parathyroids (para means "near"). These, also, produce an 
internal secretion which is related to the calcium metabolism. 
Their removal, or atrophy, gives rise to tetany, a sudden convul- 
sive contraction of the muscles, which may result in death. 
The injection of small doses of parathyroid extract usually results 
in temporary relief. The effects of too great activity of the 

parathyroids have not 
been fully ascertained, al- 
though it has been shown 
by Collip that the injection 
of parathyroid extract into 
the blood of an animal will 
increase the calcium con- 
tent of the blood while the 
removal of a part of the 
parathyroid tissue will give 
rise to a calcium deficiency. 
Pituitary gland. The 
pituitary gland weighs 
about one sixteenth of an 
ounce 'and is located at the 
base of the skull. Galen 
and Vesalius knew that 
there was a pituitary gland. 
They thought it had some- 
thing to do with the 
secretion of the nose. 
(Pituitary is from the 
Latin word pituita, meaning phlegm.) Modern experimentation 
has proved that there is no such connection or relationship. 
There seems to be sufficient evidence to justify the acceptance of 

Journal of Heredity 
Giantism and dwarfism are probably due to defective 
pituitary glands. 


the opinion that the anterior lobe or part of the gland affects 
the growth of the skeleton and the posterior part causes several 
important bodily changes. Although the hormone or hormones 
of the posterior lobe have not been obtained in pure form, in- 
jections of extracts from the lobe will cause a rise in blood 
pressure, an active contraction of smooth muscles, and a con- 
version of glycogen into sugar. Any irregularity in the gland 
affects growth, especially that of the skeleton, and the tone of the 
muscle cells of the blood vessels. Undersecretion in children 
causes them to remain small and fat. Some dwarfs are known 
to have very small pituitary glands. These dwarfs are well-pro- 
portioned, unlike the cretins with their overdeveloped heads and 
abdomens. Too active a pituitary gland in a young person 
causes an enlargement of the bones. The individual assumes 
giantlike proportions. If the gland is affected in an older per- 
son, acromegaly, a gradual enlargement of the bones of the 
head, hands, and feet usually results. A rise in blood pressure 
and the slowing of the heart beat usually accompanies the 

The adrenal glands. The adrenal glands {ad — on ; renes — 
kidneys), called suprarenal bodies by some investigators, are two 
small glands situated just above the kidneys. They weigh about 
one seventh of an ounce. The inner part of the glands produces a 
secretion called adrenin. The secretion, if there is any, of the 
outer or cortical region has never been isolated and its function is 
obscure. Adrenin, like thyroxin, can be obtained from the gland 
in a pure form. It has also been built up or synthesized by chemists 
in the laboratory. It is known commercially as adrenaline. Both 
the natural and the synthetic product tend to contract the arteries, 
thus causing an increase in blood pressure. Visceral arteries are 
affected to a greater extent than the arteries leading to the muscles. 
Adrenin also hastens blood clotting and strengthens the heart 
beat. It stimulates the liver to release the stored sugar. This 


sugar is then available for oxidation in the muscles. Thus the 
muscles may receive an additional source of energy. The amount 
of secretion from the adrenal glands is greatly increased- during 
strong emotional excitement such as fear and anger. If a person 
is badly frightened, he seems to have unusual ability to escape 
from the danger. This is due to the activity of the adrenals 
which are stimulated by the emotion, and to the fact that adrenin 
is absorbed into the blood stream in unusually large quantities. 
The pouring out of the hormone by this gland increases the 
blood pressure, strengthens the heart action, and contracts the 
visceral arteries so that the, blood supply to the muscles is in- 
creased. At the same time, the liver is stimulated to release more 
sugar than it would normally. In consequence, the blood supply 
brings more food to the muscles which are better able to respond to 
the emergency. Fatigue, too, is postponed. This often explains 
the great strength people have during an emotional crisis. The 
physical endurance of the dancing dervish is an example of adrenal 
activity. If physical activity does not result from stimulation of 
the adrenal gland, a violent nervous reaction takes place. People 
should avoid, as far as possible, situations 'that will arouse 
violent emotions, unless resulting activity is desirable. Since 

blood is withdrawn from the 
islema.o£ viscera during violent emo- 

xg-er- a.ns ^ions, grave digestive disturb- 
wSe^rts- ances may follow. It has been 

demonstrated that mental ac-' 
tivity may be seriously inter- 
fered with, causing extreme 

Certain groups of cells, known as the islands of T1 „ r , m]KnM(! 
Langerhans, are a part of the pancreas. They liei vuusiiess. 

secrete insulin. Addison's disease, charac- 

terized by great muscular weakness, darkening of the skin, low 
blood pressure, feeble heart action, and intestinal disturbances, is 
attributed, by many investigators, to degeneration or injury of 


the adrenal cortex. It is almost always fatal. Removal of the 
adrenals in lower animals always results in death. 

The commercial product, adrenaline, is used to prevent or check 
bleeding. It causes a temporary constriction of blood vessels in 
the area, which results in checking the flow of blood. In opera- 
tions for the removal of tonsils, surgeons often spray the patient's 
throat with an adrenaline solution before the operation, in order 
to prevent a great loss of blood. This is known as the bloodless 

The pancreas. The pancreas is a digestive gland secreting 
pancreatic juice which passes through a duct to the small intes- 
tines, where it acts upon the food particles coming from the 
stomach. The pancreas also acts as a ductless gland. Certain 
cells embedded in the pancreas, called the islands of Langerhans, 
produce a secretion called insulin which contains a hormone that 
is absorbed directly into the blood. This hormone stimulates 
the liver to give up its glycogen. At the same time, it accelerates 
the oxidation of sugar in the tissue cells. Thus sugar is removed 
from the blood and the body. If the islands of Langerhans lose 
the ability to produce this secretion, the sugar is not used and 
some of the extra sugar remains in the blood and some is excreted 
with the urine. The individual develops a disease known as 
diabetes. Dr. F. G. Banting and his associates discovered (in 
1922) that the insulin obtained from the normal pancreas of 
animals would produce a marked decrease in diabetes symp- 
toms. Much suffering has already been lessened through this dis- 
covery. Insulin is available for treatment of diabetes although 
it is not considered a cure. Its use must be continual, since as 
yet no method has been discovered for stimulating the defective 
condition of the organ so that it can make its own insulin. 

Other glands. The thymus is a small gland in the neck below 
the thyroid. It probably has a close relation to growth and 
possibly to sexual development. Experiments seem to prove 


that it checks for a time the development of the reproductive 
organs. It is very large in a young child, but gradually reduces in 
size during adolescence until it is very small in adults. The pineal 

body is at the base of the brain behind 
and above the pituitary. Extracts from 
this gland do not have any observable 
effect. There is some evidence, how- 
ever, that the injury or destruction of 
in a very young infant the thymus this gland in young children is usually 
is exceedingly large. followed by abnormal development. 

Beneath the diaphragm, behind and to the left of the stomach, 
is the spleen. It increases in size after a meal and reaches its 
maximum about five hours after digestion. c Then it slowly 
decreases to its former size. The cause of this activity is not 
known. This gland possibly plays a part in the formation and 
destruction of red corpuscles, because quantities of them are 
found in it. If the spleen is removed from animals suffering from 
one type of anaemia, splenic anaemia, beneficial results follow. 

The reproductive glands, also called the gonads, produce a secre- 
tion that passes through a duct, and another secretion that is ab- 
sorbed directly into the blood. Certain of the cells of these organs 
make the sex cells which leave the glands through ducts. This 
secretion is dealt with in a later chapter on reproduction. The 
normal development of the body depends upon the internal secre- 
tion of the sex glands. If the male sex glands or testes are re- 
moved from young animals, it modifies the normal course of their 
development. Thus we have the normal bull contrasted with the 
modified ox and the normal stallion with the modified gelding. 
Modified animals never acquire complete secondary sexual 

The secondary sexual characters in man include the beard, 
and the large larynx which accounts for the deep voice. After 
maturity has been attained, the changes that follow the loss of 


the internal secretions are less striking. As old age approaches, 
these glands become less active. Great prominence has been 
given experiments along the lines of postponing old age by treat- 
ment of these glands. These experiments are supposed to affect 
senescense, old age, and bring about rejuvenescence, youth and 
vigor. Various methods of rejuvenation have been tried ; such 
as, grafting glands of young monkeys on human beings or feeding 
glandular extracts. All of these methods are still in the experi- 
mental stage. Old age is the breaking down of many of the sys- 
tems in the body, and it is extremely doubtful whether glandular 
extracts will rejuvenate the entire body. To date, the persons 
who received the grafted glands showed improvement for a short 
time only. The grafted gland was, ultimately, absorbed by the 
surrounding tissues. Some scientists attribute the temporary 
youthful effects to the optimism and enthusiasm of the subject 
rather than a definite physiological effect. The experiments seem 
to have some effects, but they are too experimental to discuss as 

Questions and Suggestions 

1. Name four diseases related to the thyroid activity. State the 
amount of thyroid secretion in each disease. 

2. Discuss a diet deficiency affecting the thyroid glands. How has 
the resulting disease been controlled ? 

3. Account for giantism and dwarfism by glandular activity. 

4. Discuss all the physiological activities involved in a dancing 

5. Name two hormones used commercially. Give the use of each. 

6. Make out an outline of the ductless glands and fill in the following 
headings as far as possible : (a) Name of gland, (b) Endocrine or 
hormone, (c) Use to the body, (d) Disease resulting from over- 
secretion, (e) Disease resulting from undersecretion. 

7. During a fire, the farmer who owned the house carried a cook 
stove from the burning building. After the fire he found he could 
not move the stove without help. It took three men to carry the 
stove. How can you explain his unusual strength ? 

8. What effect does a large cheering section probably have on the 
players of a football team ? 

WH. FITZ. AD. BIO. — 14 




Mimosa, a sensitive plant. 

A leaf that catches flies. 

How are 'plants and animals adjusted to their environments f What is 
the structure of the brain f What are the functions of the brain f Is 
phrenology a science? What scientific studies have been made of the 
nervous system? 

Irritability. Plants and animals must adjust themselves to their 
environment in order to survive. Different conditions in the 
environment provoke responses in organisms. Certain of the re- 
sponses of the amoeba were considered in the discussion on the 
functions of 'the amoeba. If the response is very definite and with- 
out exception for a given stimulus, that response is known as a 
tropism. Such responses are characteristic of plants and of ani- 
mals without a nervous system. In animals with a nervous sys- 
tem, if the response is definite, mechanical, and without excep- 
tion, the reaction may still be called a tropism. For example, 
the swarming of the bees, the fluttering of moths around a light, 
and the burrowing of worms into the earth are frequently called 
tropisms. When an animal has a well-deVeloped nervous sys- 
tem, the responses are more varied and individual. The nervous 
system governs and regulates the responses to stimuli. In this 
latter case the response is called a nervous reaction instead of a 
tropism. The response of the organism, whether it is a nervous 
reaction or a tropism, is due to the activity of the protoplasm in the 



individual cells of the active organism. This property of proto- 
plasm is called irritability. The possession of this property enables 
an organism to make the adjustments necessary for living in cer- 
tain environments. Some simple experiments with plants will 

demonstrate tropisms 

Problem. What response does a plant make to sunlight f 
Prepare a box with a series of shelves arranged alternately on opposite sides 
so that they overlap each other. The shelves should be several inches apart 
and extend into the box about three fourths of the distance. Cut a small 
window in the side of the box near the top. Place a plant in a small flower 
pot in the bottom of the box. Keep the plant well watered. Place the box 
so that the window faces the sunlight and leave it for two or three weeks. 
I. A . Describe the growth of the plant, telling how it differs from the normal 
or usual method of growth of a plant. 

B. What was the value of the shelves in the experiment? 
C The response of an organism to light is called phototropism (a turning 
to light). Is the response of the shoot of the plant toward or away from 
sunlight ? 

D. What is the value of phototropism to a plant? 

Problem. What is the response of different parts of a plant to 
gravity f 

Prepare and fill a pocket garden or Petri dish with moist cotton, and place 
mustard seeds in a row across the middle of it. Keep the same edge or side 
of the garden up until the seedlings have grown to be three fourths of an inch. 
After making definite observations, turn the garden to an angle of forty-five 
degrees and keep in this position until the plants have grown another three 
fourths of an inch. Then make a second examination. Repeat this three or 
four times, in each case waiting the number of days required for three fourths 
of an inch additional growth before making a definite conclusion and before 
turning again. Be sure to keep the moisture evenly distributed throughout 
the cotton. 

I. A. Describe the direction of growth of the root ; of the shoot. 

B. After your first turning what was the result? after the second, third, 
and fourth? This response of the plant to gravity is called geotropism. 

C. How does gravity affect the growth of the root and of the shoot ? 

D. What is the value of geotropism in a plant? 



Problem. What is the response of plants to water f 

Prepare a pocket garden filled with cotton. Plant mustard seeds in a verti- 
cal line across the middle of it. Water the seeds by moistening the cotton on 
one side of the garden. Try to keep one part of the cotton always moist and 
the other part dry. 

I. A. Describe the growth of the root and of the shoot. A response to 

water is called hydrotropism. 

B. What is the value of hydrotropism to the plant? 

C. Describe any evidence in the experiment that shows whether gravity 
or water is the stronger stimulus. 

Z>. If you have ever seen willow trees growing along the bank of a river, 
describe how hydrotropism tends to affect their growth ? 

The uses of tropisms. Plants make responses to other stimuli. 
The response to chemicals is chemotropism, response to heat, thermo- 
tropism, and to touch or contact, thigmotropism. 

All the activities of living plants and animals involve a series of 
responses. As we have already learned, the responses of plants are 
definite for given stimuli. Leaves always grow toward the light, 

roots grow toward gravity, and 

stems grow away from gravity. 
Responses are divided into two 
kinds of reactions, one toward 
the force or stimulus, positive 
tropisms, and the other reactions 
away from the stimulus, nega- 
tive tropisms. In general, tro- 
pisms are protective. Without 
sunlight, the leaves would not be 
able to make starch ; without the 
pull of gravity, roots would be 
unable to anchor the plant in the 
ground. Tropisms help the or- 
ganism make the best possible 
adjustments to its environment. 

Light influences the growth of plants. 
Most stems and leaves turn toward the light 
and a large area of leaf surface is exposed. 



Irritability in man. In 
order to understand the 
reactions of man, the 
mechanism that brings 
about the reactions must 
first be studied. This 
mechanism is called the 
nervous system. It is 
often compared to a tele- 
phone system. An expert 
operator at a switchboard 
quickly brings different 
rooms in a building, dif- 

f + li mpu in n r»I+v Water, also, acts as a stimulus; sometimes it is 

ierent nomes in a City, stronger than gravity and causes a turning of roots 
different Cities, and even from their normal direction toward the water supply. 

different nations into communication by means of messages sent 
over various connecting wires. In a similar way, the various 
organs of our body are made to work together by means of nerves 
that are brought into connection by means of nerve centers. 
There are two groups of structures composing the nervous 
system : (1) the central nervous system and (2) the sympathetic 
or autonomic nervous system. These two systems are intimately 
connected with each other. 

Protection of the central nervous system. The central nervous 
system consists of the brain and the spinal cord. The brain is 
covered and well protected by' three membranes which separate 
the skull from the skull cavity. These membranes secrete the 
cerebro-spinal fluid and contain blood vessels which transmit 
blood to all parts of the nervous system. If glancing blows strike 
the skull, the movable mat of hair and skin tend to weaken the 
force of the blow. In infants, the skull bones are not completely 
joined together and, consequently, their brains are not as well pro- 
tected as the brains of adults. However, by the time the child is 



eighteen months old these bones have grown together, forming a 
comparatively firm, hard structure. The spinal cord is protected 

When the position of the growing plant is changed, gravity again determines the direction of 
the growth of the root and of the stem. 

by the spinal or vertebral column and moist lining membranes 
similar to those in the skull. The vertebral column in an adult, 
made up of twenty-six movable bones called vertebrae, permits 
flexibility, and gives protection to the delicate spinal cord inclosed. 
From both the brain and spinal cord, nerves extend to all parts of 
the body. These nerves are embedded in other tissues which 
afford them protection. 

The structure of the brain. The cerebrum. The larger part 
of the brain is called the cerebrum. It is divided into two hemi- 
spheres. The outer surface, the cortex, is composed of gray matter 

(cell bodies and syn- 
apses), and shows 
many irregular convo- 
lutions. Underlying 
the cortex are found 
nerve fibers. These 
are axons of the neu- 
rons. They make up 
the white matter. 

negative <fe* 

geotropism. g^J^ 


This plant responds to gravity : stems, negatively ; roots, 

Certain definite areas of the cerebrum are concerned with definite 
functions. These include motor areas which control movements, 



and sensory areas which are concerned with sensations. Centers 
of sensation, motor activities, speech, judgment, reasoning, mem- 
ory, and many other activities requiring 
thought are located in the cerebrum. Asso- 
ciation units link these together and make 
possible all kinds of connections. Later, in 
considering the activity of the nervous sys- 
tem, the cerebrum will be called the third 

The cerebellum. Below the cerebrum and 
partially covered by it lies a smaller por- 
tion of the brain, the cerebellum. This 
is the center of muscular coordination and 
maintenance of body equilibrium. It may 
be called the second level of the central nerv- 
ous system. 

The medulla oblongata. The brain is 
connected to the spinal cord by means of 
the medulla oblongata. This is really the 
enlarged beginning of the spinal cord but is 
considered a part of the brain. It is the 
crossing place for most of the impulses to 
and from the nerves of the brain. It con- 
tains the nerve centers which govern breath- 
ing, regulate circulation, and maintain normal 
tone of the muscles in the blood vessels. It 
controls certain acts such as sneezing, swal- 
lowing, vomiting, and blinking. 

The spinal cord. The spinal cord, nearly 
cylindrical in form, runs through the hollow vertebral column. 
It is connected with the brain by the medulla oblongata. The 
spinal cord serves as a pathway for nervous impulses from various 
parts of the body to and from the brain, and has centers of simple 


Note the relative size of 
the cerebrum in each of the 
brains. There is a close re- 
lation between size of the 
cerebrum and intelligence. 
The lower down in the ani- 
mal scale, the smaller the 
cerebrum and the lower the 



A photomicrograph of the spinal cord shows 
the white matter on the outside, and the gray 
matter in the form of anterior and posterior 
horns, on the inside. 

nervous activities which will 
be discussed later. Nerve cells 
(gray matter) are found on the 
inside of the cord and nerve 
fibers (white matter) are found 
on the outside. The spinal 
cord is called the first level of 
the central nervous system. 

Cellular structure of the 
central nervous system. The 
unit of structure of nervous 
tissue is a highly specialized 
cell called a neuron. It con- 
tains the cell body proper, the 
cyton, from which fine proto- 
plasmic processes (dendrites) extend. One of the processes may 
extend a great length and is known as the axon. The dendrites 
divide and with branches from other- nerve cells form a mass of 
extremely fine fibers. The gray matter of the brain and spinal 
cord consists of nerve cells or neurons. Collections of these are 
nerve centers. A 
number of axons 
banded together 
constitute a nerve. 
Nerves transmit 
messages from sense 
organs such as the 
eye, to the cell 
bodies of the neu- 
rons, or from the 
cell bodies of the 

neurons to muscles When the dendrites of two neurons come into contact with 

, . _ each other, they form synapses. Nerve impulses travel from 

Or glands. ill Order axon to dendrite across one of the many junctions or synapses. 



that the nervous system may function as a whole, impulses or 
disturbance must readily pass from neuron to neuron. The point 
of junction between two neu- 




rons is commonly known as a 
synapse. The sense organs, 
known as receptors, receive 
the stimulus which starts 
the nerve current. The ends 
of the nerve fibers of these 
organs are on the outside 
(skin) of the body. The 
muscles or glands are called 
effectors because they bring 
about activity. An axon 
that connects with a sense 
organ is called an in-going, 
sensory, or afferent axon; 
one that connects with a 
muscle or gland is an out- 
going motor, or efferent axon. 
The neurons possessing these 
axons may be either sensory 
or motor neurons. For ex- 
ample, when the finger is 
placed on a hot object and 
immediately withdrawn, a 
series of actions has taken 
place in the nervous system. The nerve fiber in the finger re- 
ceived a stimulus which it carried to the brain. The brain in 
turn sent out a message to the muscles in the arm and hand, so 
that the finger was immediately removed from the object. 

When neurons connect sensory with motor neurons, they are 
called associative neurons. Groups of nerve cells situated outside 

The unit of structure of the nervous system is the 
nerve cell or neuron. The control of all activities 
in the entire body is maintained by these cells. 





of the brain or spinal cord are known as ganglia. Neurons are 
linked together by means of irregular projections of protoplasm, 

dendrites, establishing synapses. 
The nature of these contacts is 
not known. They may be com- 
pared with contacts made by two 
electrically charged wires. The 
type of energy establishing the 
contacts in a synapse is nervous 

Autonomic nervous system. 
This system is also called the 
sympathetic system or self-acting 
system. In front of the spinal 
cord, and lying parallel to it on 
either side of the vertebral col- 
umn, are two rows of ganglia, 
connected with one another by 
nerve fibers. Certain large gan- 
glia, called plexus, are also part 
of this autonomic system. Three 
of the plexus are the cardiac 
plexus in the thoracic cavity, the 
solar plexus in the abdominal 
cavity, and the hypogastric plexus 
in the pelvic cavity, but they 
connect with many other small ganglia in the thoracic and ab- 
dominal regions. The autonomic system transmits some of the 
disturbances of the central nervous system to the heart, glands, 
and involuntary or plain muscles. Since the viscera (internal 
organs) in general are made up of smooth muscle, it follows that 
the so-called automatic mechanisms of the body, such as, the beat- 
ing of the heart, the contraction and dilation of the muscles, and 

••• hypo- 

The autonomic nervous system consists 
of a series of ganglia, most of which are 
included in two chains that lie parallel to 
the spinal column. These are connected 
with nerve centers in the spinal cord. 

A very large and unpaired ganglion is 
called a plexus. 



the secretions of various glands, 
are largely under the control of 
the autonomic system. Emotions 
affect the autonomic system, and 
consequently circulatory and glan- 
dular disturbances follow or ac- 
company emotions. If a plexus is 
injured, a violent reaction in cer- 
tain internal organs would natu- 
rally follow. 

Studies of the nervous system. 
Scientists have been able to show 
that there are many similarities in 
the nervous systems of man and other vertebrates. Probably 
one of the outstanding differences is the fact that man's cere- 
brum is generally larger and heavier, proportionately, than that 
part N of the brain of any lower animal. The lower down the 



*: spinal 
-' nerves 

— ctiain, of 

of autonomic 

The ganglia of the autonomic nervous 
system are connected with the central 
nervous system by nerve fibers. 







There are three types of neurons. Some take sensory stimulations into the body, others 
take motor or glandular stimulations out to muscles or glands to bring about a response. A 
third type, known as the associative neuron, may lie between the other two types of neurons and 
set up connections between them. 


animal is in the scale of classification the smaller is the cerebrum. 
The convolutions or creases in man's brain are . more intricate 
and deeper than those found in lower animals. These convolu- 
tions give greater brain surface and contain more functioning 
neurons. Scientists once thought that one man was more intel- 
ligent than another because one had a heavier brain than the 
other. But this does not seem to hold true. The brain of 
Cuvier, a great scientist, weighed about four pounds, while that 
of Gambetta, a French statesman, weighed only two and a half 
pounds. Since mental defectives have been found with brains 
weighing more than four pounds, weight alone does not mean 
everything. The size and weight of a person must be taken into 
account when considering weight of brains. 

Neurons never increase in number. The only growth possible 
is the setting up of connections or synapses among the different 
neurons. The more connections or synapses that are made, the 
greater will be the number of mental processes, which is a factor 
in determining the intelligence of animals. The ability to make 
connections easily seems to be an inherited character. This may 
account for the fact that some families have members more intel- 
ligent than those of other families. 

One of the methods of studying the nervous system is through 
experimentation with lower animals. Flourens and others have 
observed that if the cerebrum of a pigeon is removed, the pigeon 
loses all voluntary or conscious action. It will not move toward 
food nor away from danger. However, if food is put into its 
mouth, it will swallow. When the cerebellum alone is removed, 
balance and coordination become disturbed. The pigeon, if 
placed on the edge of a table, will fall. It has difficulty flying be- 
cause of a lack of balance and muscular coordination. Its volun- 
tary activities, however, are intact. It experiences desire for food, 
fear of danger, and other sensations. If the medulla is removed, 
respiratory, circulatory, and heart actions cease and the bird dies. 



A second method of investigation is by clinical observations and 
examination, and autopsies. Doctors observe and examine the 



1 % 






According to clinical investigation and animal experimentation, the control of certain physical 
functions is localized in definite areas of the brain. There is considerable investigation at 
present as to whether there is general control of these functions as well as definite control. 
The localization of intelligence, including thinking, association, and memory, is still open to 

symptoms of people that show nervous disorders, and in many 
cases are able to determine the cause of the trouble. When such 
patients die and autopsies are performed on the bodies, the doctors 
can, in some cases, link up the nervous disorder with the part of 
the nervous system showing disease. For example, if a person 
had been paralyzed on the left side of the body, the autopsy will 
show whether an obstruction, probably in the form of a blood 
clot, is on or near the part of the brain controlling muscular 
movements. If a person were blind, the autopsy may show injury 
to the area of the brain controlling vision. 

Certain scientists, through experimentation and study of normal 
and of diseased brains, have localized certain areas in the brain. 
For a time people carried the idea of localization to an extreme. 


They thought that a "person's aptitudes and traits of character 
could be told from the swellings over these various areas. If one 
man had a swelling over the vision area, they assumed that he 
could see better than another. If he had a high forehead, they 
reasoned that his powers of judgment must be better. Thus the 
pseudo-science of phrenology arose. Phrenology, as such, has 
been disproved. Careful investigations have shown that the brain 
does not conform exactly to the shape of the skull and that bumps 
or enlargements on different heads are usually malformations of 
the skull and not brain enlargements. 

Questions and Suggestions 

1 . What is a stimulus ? What is a response ? 

2. Discuss an experiment illustrating phototropism ; geotropism; 

3. What is the value of tropisms to the plant? 

4. State the difference between a tropism and a nervous reaction. 

5. Name a function of the central nervous system. 

6. Discuss the protection of the brain and spinal cord. 

. 7. Describe the structure and the function of the cerebrum. 

8. Discuss the function of the cerebellum ; the medulla oblongata ; 
the spinal cord. 

9. Describe in detail the unit of structure of the nervous system. 

10. Draw and label a neuron. Name and define three types of 

11. What are nerve centers and ganglia ? 

12. Compare the brain of man with the brain of lower animals. 

13. Discuss two ways of studying the nervous system. 

14. Describe the structure and function of the autonomic nervous 

Supplementary Readings 

Gates, A. I., Elementary Psychology (The Macmillan Co.). 
McDougall, W., Outline of Psychology (Charles Seribner's Sons). 




Ancient idea of the human 
nervous system. 

Present idea of the human 
nervous system. 

What mental activities are learned and wliat are instinctive f 
is a habit t What is the best method for learning facts t 


When tropisms were discussed, the importance of stimuli was 
stressed. As in plants and lower animals, it is a stimulus in a 
higher animal that starts the nervous impulse which results in a 
typical reaction. This impulse may be any one of three types of 
mental activities : (1) inborn automatic, (2) acquired automatic, 
and (3) voluntary. 

Reflex activities. There are certain motions and acts that a 
baby performs soon after it is born. These responses are simple 
reflexes or inborn automatic activities. The child does not have to 
learn or acquire them. Some of these responses may involve the 
brain, while others are controlled only by the spinal cord. The 
child comes into the world equipped with pre-formed connections 
or tendencies to connections in his nervous system. In other words, 
nervous pathways or patterns are already set up. A new-born 
baby that has not learned to think will pull his foot away if 
pricked with a pin. He will sneeze if his nostrils are tickled with a 
feather, and will grasp a finger if it is placed on the palm of his tiny 
hand. Each of these responses to the given stimulus is a reflex. 
If a person swings one leg freely over the other and taps it just 



below the knee cap, the tap will cause the knee to jerk. In this 
experiment, the stimulus is received by a nerve ending in the skin. 
The stimulus starts an impulse which travels along a sensory 
neuron into the spinal cord. There, this sensory neuron links up 
with an outgoing motor neuron by means of a synapse. The out- 
going neuron conveys the impulse to a muscle in the leg, which 
causes the knee to jerk. In some way, the in-going sensory stimulus 
is changed into an outgoing muscular reaction. The sense organs, 
in this case " touch spots " in the skin, receive the stimulus and are 
the receptors. The muscle effects the reaction and is the effector. 
The pathway of the receptor, composed of the afferent axon, affer- 
ent cyton, synapse, efferent cyton, efferent axon, and the effector 
make up the reflex arc. Any reflex arc involving the central 
nervous mechanism begins and ends in the outer part of the body. 

Types of responses. The simplest response activities involve at 
least two neurons. Experiments have been made with frogs 
whose brains have been severed from their spinal cords. Such 
frogs lose all conscious activities, but are still capable of making 
certain reflexes. If the toe is pinched, the leg is withdrawn; 
violent pinching causes a distinct jump. If a paper wet with 
dilute acetic acid is placed on the skin of the leg, the frog makes 
movements to brush off the paper. 

If the foot of a sleeping baby is tickled, the foot is withdrawn. 
This is a reaction or reflex of the first level. The impulse, caused 
by the stimulus, passes into the spinal cord and out again without 
involving any other connections. The knee jerk is another ex- 
ample of a reflex of the first level. But, if the blow on the knee 
is severe enough, the person may gasp or. scream or balance him- 
self to preserve his equilibrium. He may even show an increased 
heart beat. The centers of respiration and circulation are stimu- 
lated, and balance and coordination are brought into the action. 
This response is of the second level. A number of neurons enter 
into this activity. Some of them are sensory and a great many 


are motor, which result in a number of reactions. Reactions of 
the second level are more complex than those of the first level 
and will involve parts of the 
body somewhat distant from 
the point of stimulation. 

When the knee jerk 
arouses thought or delibera- 
tion, it is classified as a third A reflex arc is traversed when the finger touches 
11 p i a nail. The sense organ in the skin is stimulated, 

level response, r Or example, the stimulus is carried over the afferent or sensory 
if +Tip Klnw i« en qpvpw neuron through a synapse to a motor neuron. This 
ii u.ic uiuw io bu bcvcic ends in a muscle which contracts and causes the 

that one would rub the in- fln « er to be puUed away * 
jured spot or examine it deliberately, certain neural connec- 
tions would be made in the brain. Such consequent thoughtful 
activities attend the reflex so closely that they are sometimes con- 
sidered a part of the reflex. Such reaction is called an activity of 
the third level. 

Conditioned reflex. A baby is born with the pathways for a 
certain number of reflexes already established. When certain sense 
organs are stimulated, the impulses travel along these pathways 
until they reach muscles or other mechanisms, which carry on the 
processes essential for maintaining life ; such as, sucking, digesting 
of food, crying, coughing, and moving. When these responses 
are caused by other than the original stimuli, they are said to be 
modified or conditioned. For example, Pavlov, a Russian physiol- 
ogist, observed that the secretion of saliva in a dog is a reflex act, 
resulting from nerve pathways established in the dog at birth. 
The appearance of food or the taste of food in the mouth acts as the 
stimulus, and the flow of saliva is the response. If the same person 
always feeds the dog, the saliva of the dog will, after a certain 
number of times, flow at the sight of that person even though no 
food is given. The stimulus in this case is the sight of the person, 
not the food, and the response is the flow of the saliva. The 
response occurs in the hungry animal even when it can neither see 

WH. FITZ. AD. BIO. — 15 



nor smell any food. The animal has evidently acquired a new re- 
flex path. The acquired reaction is conditioned upon a memory 

association which con- 
nects the presence of a 
certain person with the 
eating of food. 

In another experiment, 
a bell was rung, and ex- 
actly two minutes later 
food was given a dog. 
Ultimately, after the ex- 
periment had been con- 
tinued a long time, the 
saliva flowed in the dog's 
mouth exactly two min- 
utes after the ringing of 
the bell even though no 
food was given. This could be carefully measured because of 
a little tube that was injected into the duct leading from the 
salivary gland of the dog. Saliva could be seen flowing from the 
duct exactly two minutes after the ringing of the bell. Sparrows 
usually build nests in the gutters and holes in barns and houses. 
Building the nest is inborn, but buildings have not existed as long 
as nest-building, so nesting in houses must have become conditioned 




The three levels of the nervous system are shown 
here. The first level is in the spinal cord, the second 
level is in the cerebellum, and the third level is in the 


by buildings. Conditioned 
responses depend upon 
associations formed in the 
cerebrum. Injury to a 
certain part of the cere- 
brum of a dog with a con- 
ditioned response has caused the ability of the animal to respond to 
the stimulus to be entirely destroyed. 
The original reflexes that are a part of the organism at birth are 

sensory neuron 

In a reflex of the first level, the center of control is 
the spinal cord. This is the simplest type of reflex. 
The response is usually very simple. 


evidently not fixed and invariable but are flexible and modifiable 
and may become changed or conditioned by factors in the environ- 
ment. The organism begins to in&bm'm mvscie 
relate factors in the environment 
to his activity. This results in 
the changing of the original re- 
flex. Certain acts may be con- 
sciously inhibited, that is, di- 
verted or blocked. For example, 
a child instinctively makes known 
his wants by crying. He has 
learned that when he cries, he has Teuton S£> rfl 1 * effector 

always been picked Up. One day, In response of the second level, centers 
U XX J j.l~ • J j. m tne spinal cord and mid-brain exercise 

ne Unas that Crying does not control. A number of activities will re- 
bring the desired attention. He sult ' 

stops after a while, and, in time, learns to express his wants in 
another way. The changing is due to consciousness. It probably 
explains the beginning of the learning process or conscious acts. 

Voluntary activities. Any act involving will or thought is a 
voluntary act. The name " voluntary " refers to the will. All 
activities, excepting the so-called inherited reactions, performed 
for the first time are voluntary acts of the will. When the 
activity requires attention, memory, judgment, or association, a 
great many associative neurons are used. For example, the hand 
is put in water and is held there while a decision is made as to 
whether the water is of the desired warmth. Then the hand is 
withdrawn. The sensation is received by the skin as the receptor. 
The impulse travels along an afferent axon to the spinal cord, up to 
the brain. A number of neurons located in the brain are stim- 
ulated, bringing about a condition of consciousness, and resulting 
in attention. Meaning becomes attached to the sensation that has 
been received and a mental decision is possible. A comparison may 
be made with previous water used in washing ; the thought may 




occur that injury will result in casejt is too hot; a consideration 
of the fact that cold water will not cleanse may be involved. 
Finally a decision is made. Then a connection is made with a 
motor neuron. The impulse goes down the efferent axon to the 
muscles in the hand and the arm, which are the effectors of the 
activity and the hand is withdrawn from the water. In many 
instances, the learning of facts such as rules of grammar is im- 
possible without attention. Attention is partly dependent upon 
inborn tendencies and partly upon acquired habits. The more 
closely the activity is related to the child's life and the more 
associations he can make, the easier it will be for him to remember 
the facts. For instance, if a child lives in a city, it will be easier 
for him to understand the problems of city government and traffic 
conditions, than for the child who has always lived in a rural 


Acquired automatic ac- 
tivities. Activities which 
are learned in a person's 
lifetime, but have become 
automatic through repe-. 
tition, are acquired auto- 
matic activities. For ex- 
ample, brushing the teeth 
is an act that had to 
be learned. By directing 
attention and thought on 
the action the first few 
times the teeth were 
brushed, definite tech- 
nique and skill were soon 
gained. The receptor 
was the gums of the mouth. When the toothbrush was placed 
in the mouth, a sensory axon took the impulse into a sensory 

of second 

Rector* ©P 

thira. ' 

effected of 
fttwt Wei 

A third-level response uses neural connections in 
the brain. Psychologists think that all learned reac- 
tions are dependent upon connection established in the 
brain level. 


neuron of the cerebrum. As the child thinks whether he shall 
brush the teeth, up and down or across,, whether his mouth should 
be open or closed, whether he should lean over the basin or not*, 
connections are set up among association neurons. Finally, he 
comes to a decision. An impulse is sent along an efferent axon 
down the spinal cord and into the muscles of the arm which are 
the effectors. The actual brushing of the teeth is the motor 
response. The correct response was consciously made. This is 
an act of the third level involving the cerebrum. After the teeth 
have been brushed a number of times, the decisions and the asso- 
ciations are no longer necessary. While the act was conscious, 
inhibitions Jn the nervous system blocked certain paths of con- 
duction between the sensory stimulus and the motor response. As 
the act was repeated, time after time, these inhibitions disappeared, 
and the act was easier to perform. The more times the impulse 
passed over the pathway of discharge, the less was the resistance 
to it. After this reaction was learned a synapse was set up be- 
tween the afferent and efferent pathways, leaving out some of the 
association neurons. In some habits the pathway is essentially the 
same, but consciousness is omitted. It has become automatic and 
has descended to the second or possibly the first level. It is now 
an acquired automatic activity involving no thought and is com- 
monly called a habit. Habits are frequently defined as acts which 
were first done in a typically voluntary way, but after sufficient 
repetition they are done in a comparatively reflex way. Memory 
is most important in changing conscious acts into habits. 
. Importance of the autonomic system in nerve activities. The 
internal organs, in general, are under the control of the autonomic 
nervous system. The autonomic system controls the contractions 
and relaxations of the smooth muscles. It regulates glandular ac- 
tivities and heart action. Emotions activate the autonomic sys- 
tem. If an emotion such as fear or anger accompanies a reflex act, 
habit, or a conscious act, the autonomic system enters into the 


activity. There will then be attending respiratory, circulatory, 
and glandular activities. For example, a rabbit sees a cat and 
fries to escape. The sensory stimulus is the sight of the cat while 
the reaction is the motor act of escaping. Because fear attends 
this voluntary act, the autonomic centers of the rabbit are stim- 
ulated and their resulting activities favor the response of out- 
witting the cat. The bronchial tubes of the frightened rabbit are 
relaxed and rapid breathing is made easier. The contraction of 
blood vessels in the viscera and the increased heart action forces 
more blood into the skeletal muscles. Thus, extra oxygen and 
fuel are supplied to the muscles. The 'nerves stimulate the 
adrenal glands which pour out their secretion into the blood, 
causing the liver to give up more sugar into the blood, as well as 
increasing the endurance and strength of the muscles and reducing 
the activities of digestion. The rabbit has more energy than 
normally and is able to run faster from the cat which is activated 
purely by the instinct of hunting. But, if the cat is aroused by 
a strong feeling of hunger, we would find in her activities very 
similar to those in the rabbit. In this case, the probability of 
escape by the rabbit would be lessened. 

The nature of the nerve impulse. The nature of the nerve 
impulse is not fully understood. The speed with which it travels 
along a motor nerve fiber is about three hundred and ninety feet 
per second. The time elapsing between the application of a 
stimulus and the response varies in different individuals and in 
the same individual under different conditions. It depends upon 
the strength of the stimulus. If the stimulus is very strong the 
response will be prompt. If the stimulus is weak the response 
is not made or is made very slowly. The time of reacting is 
dependent upon the nature of the stimulus. For example, the 
response to a person walking toward you is quite different from 
the response given when an automobile comes toward you. The 
time is also affected by the number of synapses through which the 


stimulus has to pass. If the nervous pathway is long, a propor- 
tional length of time is required for a response. Removing your 
hand from a hot stove requires less time than deciding which way 
to jump when you find yourself in the path of a fast moving car. 

The importance of reactions. The patterns of behavior formed 
almost immediately after birth are called instinctive or innate acts. 
These include the avoiding reactions such as struggling when 
held, and withdrawing from or rejecting anything that is causing 
discomfort, as moving the leg if it is being pinched; and the 
approaching reactions or movements caused by hunger and by the 
stimulation of certain sensitive parts of the body, such as, tickling 
the bottom of the feet or rubbing the back. These reactions or 
established patterns are frequently modified to meet changing 
conditions. For instance, a small child will usually push away 
or strike at a person who annoys him, but later he will modify 
his tendency because the group he lives in demands a different 
method of reaction. He will learn to respond to reason and not 
follow his instinctive desire to fight. 

Habit formation. When voluntary activities are made habitual, 
they are performed more easily and quickly. When completely 
established, they act the same as instincts. When activities be- 
come habits the brain is not needed and it is then set free to make 
new responses or activities. This results in the growth and de- 
velopment of the mind or consciousness. If the attention were 
concentrated on the daily performance of brushing the teeth, 
dressing, walking, and other necessary activities, the mind would 
be occupied continuously on acts that are necessary for mere 
existence. The possession of useful habits sets the mind free to 
attend to the gaining of new knowledge. Individual progress 
may be said to be dependent upon the ability to acquire habits. 

There are three rules for making conscious activities, such as 
combing the hair, or starting an automobile, habitual. First, 
there must be concentration on the performance of the act. 


When there is a real desire to build the habit, it is more easily 
formed. Second, the activity must be repeated a number of times 
under exactly the same conditions, permitting no exceptions to the 
performance. Third, the act becomes automatic niore quickly if 
feelings of satisfaction attend the performance. If any annoyance 
accompanies the performance, it delays the forming of the habit. 
If exceptions are made in the type of reaction, judgment again 
enters into the performance and it continues as a thoughtful act 
rather than a habitual one. In performing the act each time in 
exactly the same way, the same nerve padi is traversed. Then 
when the stimulus is received, the impulse goes more quickly over 
the pathway, and synapses connect up with greater facility. 

In order to break a bad habit, there must first be a sincere desire 
to get rid of it. The activity must be brought back to conscious- 
ness so that the will may be directed on breaking it. For example, 
in order to break the habit of biting the nails, red pepper may be put 
under the nails. The sharp biting effect on the tongue will bring 
to consciousness the fact that the nail is in the mouth. Each time 
the person realizes that the nail is in the mouth, he must take it 
away from the teeth and there must be no exception to this reac- 
tion. The person who says he cannot break himself of a bad 
habit means he does not want to break it. If the growth of the 
nail and the improved appearance of the hand brings satisfaction, 
the habit of refraining from biting the nails will be more speedily 
established. The most effective way of breaking a bad habit is 
to substitute a good habit which will be more satisfying than the 
bad habit. For example, if a boy has formed the habit of standing 
on a street corner in the evening, he may find that joining an 
athletic club will be so satisfying to him, because of its activities 
and congenial companions, that in a short time his old habit has 
lost its influence altogether. It is not wise to ever perform an 
idle or vicious voluntary act, for if a synapse has once been es- 
tablished between two neurons in performing an act, it is easier 


for the nerve impulse to go over this pathway a second time. 
There is always the danger of an undesirable voluntary act be- 
coming habitual. The years of childhood are the critical ones in 
habit formation and, therefore, in character building; childhood 
habits form the basis for later conduct. If the acquired habits 
are later found to be undesirable, it is necessary to make substitu- 
tions and this is a waste of mental energy. Consequently, it is of 
the utmost importance to build correct habits by the proper con- 
ditioning of reflexes in the beginning. 

To a large extent, mental growth results from acquiring a large 
number of useful voluntary activities. Prpbably every one has 
the same number of neurons. There is an infinite number of 
possible connections among them. The same neuron may link 
up with several others and this may result in a great many different 
activities. As each new act is performed, a new combination of 
neurons is connected by means of synapses. The more synapses 
are made, the greater will be the growth in experience, judgment, 
memory, and reasoning. If any voluntary act which is useful 
can be relegated to the realm of habit, it will give greater oppor- 
tunity for acquisition of new voluntary acts. 

Problem. The study of nervous activities: 

List twenty simple activities performed by you in one day. Next to each 
activity put the class in which it belongs : inborn automatic, acquired auto- 
matic, or voluntary. 

I. Which of the voluntary activities listed would be desirable as habitual 
ones? Why? 

A. What prevents them from becoming habits? 

B. How may they be changed into habits? 

II. How can you improve the performance of any act in your life? 

Questions and Suggestions 

1. What is a reflex arc? Make a labeled diagram of the reflex arc. 

2. Name three types of nervous activities. 

3. What is the value of reflexes to the organism ? 


4. To which activity is a tropism comparable ? 

5. Draw and label a diagram of a reflex activity. 

6. Explain and give an example of the conditioned reflex. What 
scientist has been investigating it ? 

7. How could you make learning to swim a habit ? 

8. Make a labeled diagram of an acquired automatic activity. 

9. Explain how the habit of biting the nails may be broken through 
(a) inhibition, (b) substitution. Explain which method is the more 
desirable method. 

10. Why is it possible for people to break themselves of bad habits, 
if they have an earnest desire to do so ? 

11. Discuss the advantages and disadvantages of adopting a child 
of six months ; of five years ; and of fourteen years of age. 

12. Give examples, from your own experience, of habit formation, 
and discuss the importance of attitude as an aid and as an interference. 

13. What is the value of a habit of regularity ? Of concentration ? 
Of thoroughness ? 

14. What is the relation between habit formation and vocational 
success ? 

15. What is the importance of voluntary activities ? 

16. What is the function of the autonomic system? 

17. Discuss the value of basing education on what a child wants 
to know rather than on what an adult thinks he ought to know ? Should 
a child study only those things he wants to know ? 

18. What is the relation of interest and attention to understanding ? 

Supplementary Reading 
See Chapter xxii. 



Some like to paint — 

Others enjoy a swim. 

What relation have psychologists found between intelligence and suc- 
cess f How can the nervous system be kept in good condition? 
What may be the effects of worry, fear, temper, and introspection f 

The ability to meet and solve the problems of one's life without 
needless worry, leads to serenity, contentment, and happiness. 
The solution of problems brings a joy of achievement that is con- 
ducive to greater success. The boy whose problems are decided 
for him does not find the contentment nor achieve the poise that 
is attained by the boy who faces and solves his own problems. 
Poise is usually considered one of the constituents of. success in 
the varied and complex life of the present day. 

Intelligence. Intelligence may be defined as the native capacities 
of a person to learn, to reason, to exercise mental control, and to 
solve his life's problems. Can a child be apparently dull or back- 
ward for a number of years and suddenly become highly intelli- 
gent? Scientific experimentation seems to prove that certain 
mental capacities are native or inborn. If a child of six years of 
age is found, experimentally, to be of average intelligence, when 
measured by certain tests, he will, with very rare exceptions, be 
found to have average intelligence at seven years, eight years, and, 
in fact, all through his life. If a child of six years tests below aver- 
age, the chances are that he will remain at that level all through life. 





15$ 20# 



46^ '9% 



Intelligence of these, meru 
as ^termme5Llythe0lphatfest 

The Army Alpha test was given to 1,700,000 men in 
the United States army in the World War. It con- 
sisted of 212 questions. Grade A was given to those 
answering correctly 135 or more of the 212 questions; 
grade B for 105 to 134 correct answers. A was earned 
by only 4.5% of the men. Compare the results attained 
by the other groups of men as shown in the table. 

The scientific measurement of intelligence, most frequently used 
as individual tests, is a series of performance tests arranged in the 

order of difficulty. The 
first of such tests was 
worked out by two French 
psychologists, Alfred 
Binet and Theodore 
Simon. These tests have 
been, revised by different 
persons in America, and 
among these revisions is 
one by Terman, known 
as The Stanford Revision 
of the Binet-Simon Scale. 
This scale includes tests of 
memory, language com- 
prehension, size of vocab- 
ulary, knowledge of familiar things, judgment, and many other 
mental tasks that are a part of every child's experience. Stand- 
ards, to show what children of certain ages should know, have been 
established by comparisons of the results or ratings made by chil- 
dren of definite ages in all sections of the country. For instance, 
there are a certain number of questions that a six-year-old child is 
supposed to answer correctly. If a particular child of six answers 
less than this score, he is said to have a mental age, M.A., of four 
or five, or whatever age that score is supposed to measure. If he 
answers more than the required number, he may have a mental 
age of seven, eight, or even more. Thus there are tests ranging 
in difficulty from those for a three-year-old child to those given 
to an adult. For the practical purpose of measuring progress in 
school the intelligence quotient, I.Q., is used. This is obtained by 
dividing a child's mental age by his age in years. This quotient 
will usually remain fairly constant from year to year, for his men- 



tal age will grow or increase as he becomes older. The average in- 
telligence quotient for any given age is 100. For example, a pupil 
has a mental age of six, according to the Stanford Revision Scale, 
and his age in years is six. Divide his M.A. 6 by his real age 6 
and the intelligence quotient will be 1.00. (This I.Q. is usually 
expressed without a decimal, as 100.) Another pupil of 6 has a 
mental age of five and a half and his real age is six. Dividing his 
mental age, five and a half, by his age in years, six, we find that 
he has an intelligence quotient of 92. If a pupil's mental age is 
eight and his age in years (chronological age) is six, his intelligence 
quotient is 133. The I.Q. of the average high school graduate 
probably ranges from 90 to 105. 

Relation of intelligence to progress in school. In general, 
pupils who have low intelligence quotients have difficulty in 
making progress through 
school. When pupils with 
high intelligence quotients 
have difficulties with their 
studies, it is usually due to 
physical defects, irregular 
attendance, late entrance, 
refusal to study, or some 
other remediable condition. 
If a child is retarded in 
school, even though he puts 
forth sincere efforts, and 
there is no remediable con- 
dition interfering with his 
school work, then he should 
be given a different type of 
schooling. Various voca- 
tional schools are endeavoring to provide courses for such children, 
so that they may take subjects which they can understand and in 


left school 4 gfcacte 



<o • 

27# 7+8 - 

25?^ aft*r8 - 


enteral Ki^h school 


gto&xxoted. college 

The schooling of the American population has 
been graphically described in the above table. This 
is based on a report of the Department of Labor. 
Compare the distribution of schooling in this table 
with the distribution of intelligence in the preceding 





which they can achieve success. 
If a child is permitted to fail 
term after term, he falls into 
an attitude of mind which de- 
stroys his confidence and he 
makes only a half-hearted 
effort to succeed. He gets the 
habit of failing. The pupils 
who reach high school are, to 
a certain extent, a selected 
group, because the dullest pupils 
have become discouraged and 
dropped out. Education re- 
sults in the growth of experi- 
ence or mental age, but not 
native ability. 

Relation of intelligence to 
vocations. Individuals who 
rate low in the intelligence tests are not, necessarily, undesirable 
members of society. There are relatively few children so dull that 
they cannot succeed in some line of work. Many failures and 
much discontent are due to the fact that boys and girls sometimes 
enter vocations that require too much or too little intelligence in 
relation to their mentality. 

The leg muscle of a freshly killed frog is at- 
tached to a lever. It is stimulated through the 
nerve by means of a make and break electric 
current. A tracing of the contractions is made 
on a, revolving drum. At first the contraction 
is very decided and regular. Slowly the re- 
sponse decreases until the muscle ceases to 
react. Rest or washing the muscle will start 
the response anew, but in a short time fatigue 
again is apparent. 

Record made on a revolving drum by a stimulated frog's muscle. 

In an experiment conducted by J. K. Flanders and reported by 
Terman, the intelligence of a group of employees of an express 
company was tested. These people were employed to do work 
that required about the same level of mental ability. It was 



"found that their intelligence, that is, their I.Q., ranged from sixty- 
two to one hundred and four. This work could have been done 
efficiently by persons with scores of ninety. C. W. Waugh^ave 
intelligence, tests to eighty-two street-car motormen and con- 
ductors. The investigation showed a range of intelligence from 
sixty-five to one hundred and ten. A score of eighty to ninety 
was probably sufficient for a person to do this type of work well. 
Those with higher intelligence did not do more work nor do it 
more efficiently than those of lower intelligence. One of the 
men scoring low had a serious accident on his car. It is a 
fairly well-established fact that a motorman or conductor with 
an I.Q. of less than/ seventy-five is, as a rule, an unsafe risk. 
There is a big economic loss, to the company as well as the indi- 
vidual, in employing men of high intelligence to do work that 
could be done as well by men with less intelligence. Educators 
should direct those students of highest I.Q. ratings into lines of work 
which will require superior intelligence, and those of mediocre in- 
telligence, low I.Q., into lines 


of work for which they are 
fitted. At present, there is 
too great a waste of mental 
ability by men and women 
filling positions that could be 
competently filled by persons 
of less ability. Students 
studying professional subjects 
should be those of fairly high 
intelligence rather than 
merely those with money 
enough to pay for such train- 

A healthy mind. The nervous system, like the other systems 
of the body, is kept in the best possible condition if the body is 

fc^toplasm^ 7 

A tired nerve cell (B) shows fewer chromatic 
granules than a rested nerve cell (A). 




Idleness does not bring satisfaction for any 
great length of time. It is, frequently, the result 
of bad habits and usually, if not always, leads to 

kept healthy by fresh air, good 
food, sleep, rest, sunlight, and 
exercise. The nervous system 
is probably more sensitive to 
the lack of any one of these 
conditions than any other sys- 
tem in the body. A change of 
activity is frequently bene- 
ficial. Otherwise,, a person 
may become physically as well 
as mentally fatigued, thus 
greatly reducing his efficiency. 
Every person should have a 
hobby and follow it as much as 
possible. A hobby that takes 
him out of doors is more de- 
sirable than one that keeps 
him indoors. People with hobbies are usually able to make use 
of their leisure time in a way that is enjoyable as well as bene- 
ficial to them. 

Fatigue. Prolonged or continued contractions of muscles in 
any kind of work result in fatigue. This condition is almost 
always followed by a steady decrease in efficiency. The feeling of 
fatigue is very complex and is often associated with such mental 
states as lack of interest, lack of will power, and distaste for the 
work. Work done under compulsion usually results in fatigue 
more readily than when interest is a part of the work. This is one 
reason why e,very one should do the kind of work which he really 

Experiments have shown that if some blood of a fatigued animal 
is injected into a rested one, signs of fatigue are promptly produced 
in the second animal. Fatigue is probably due to an accumula- 
tion of waste substances in the cells and in the blood, resulting from 



the oxidation process. If these accumulate faster than the organs 
of excretion can eliminate them, they are likely to act as poisons. 
At the same time, the food material in the cell becomes exhausted. 
Because all bodily activities are slowed up during sleep, the sleep- 
ing organism has a chance to eliminate the accumulated wastes. 
The repair of all tissues goes on during sleep. It is the muscle 
cells and brain cells, particularly, that become fatigued. In 
monotonous work the same neurons are constantly being used. 
This work should be counterbalanced with some kind of recrea- 
tion. Rest and play balance mental work because different path- 
ways are traveled. Fatigued synapses offer resistance to impulses. 
This naturally results in inefficiency or lack of activity. A high 
school boy or girl should sleep, approximately, nine hours a night 
in order to efficiently restore fatigued nerves and muscles. 

Mental poise. Mental hygiene has for its object the promo- 
tion of mental poise and serenity, and the prevention of mental 
disorders. Nervous instability is shown by a predisposition to 
strong emotions that are easily aroused and are only controlled 
with difficulty. Worthless n-* 
nervous activities should be 
eliminated as far as possible 
by cultivating proper atti- 
tudes. Worry and fear stimu- 
late certain parts of the auto- 
nomic nervous system and may 
have injurious physiological 
effects. Strong emotions tend 
to stimulate the adrenal glands, 
causing the withdrawal of 
blood from the viscera. This 
may result in serious digestive 
disorders. Worries exercise neurons with no worthwhile gain. 
Frequently, the worry is over an act that is beyond control. For 

WH. PITZ. AD. BIO. — 16 

A hobby gives one a satisfying way of spending 
leisure time. The more interesting and novel is 
the hobby the greater will be the resulting satis- 



example, people worry whether or not it will rain ; whether or not 
they will be struck by lightning ; whether or not they will be hit 

The frame of mind with which one enters into an activity directly affects the results. Cheer- 
fulness towards duty is a desirable attitude to cultivate as it tends to* bring about greater 
efficiency and mental poise. 

by an automobile. If a condition is recognized as beyond control, 
thought should be put out of mind. Nothing can be done 
about it. Mental energy should not be wasted. 

Another type of worry is closely akin to fear. Some persons are 
afraid they will not pass an examination ; others are afraid of the 
dark, or of a neighbor's criticisms. The only way to control these 
worries is to face them fairly and think them through to a conclu- 
sion. In practically every case, the fear or worry would not exist if 
the problem had not been avoided in the beginning. For example, 
the refusal to study will, in most cases, result in a fear of failure. 
When children face the painful consequences of conduct, accept 
failure or blame at face value, decide about problems rather than 
evade issues, face their difficulties squarely, and make a decision, 
they achieve mental poise. If the nervous energy consumed in fear 
were put into solving the problem, it would be used to a better 
advantage and the person would be happier. If one is afraid of 
failing in an examination, he should find out the cause of his fear. 
Possibly, the solution is to work harder. Possibly, the pupil is 



beyond his grade. If so, he should recognize the conditions and 
ask to be demoted. The effect of the failure is worse than^the 
demotion. If afraid of the dark, one should investigate the dark 
place and see how unreasonable is the fear. If the mind is kept 
occupied with useful and cheerful thoughts, fears and worries 
disappear. Fears in children as well as in older persons may be 
overcome by a quiet reassurance and a reasonable, sympathetic 

Bad temper is frequently an excuse for inefficiency. It is a way 
out of an annoying situation. If, instead of giving way to moodi- 

Strong emotions are frequently shown in facial expressions. Note the facial expressions in 
the picture and try to determine what emotion is registered in each. 

ness or temperament, the person tries to understand the difficulty 
confronting him and tries to think out a solution, a normal re- 


sponse will follow. These normal responses help to develop 
proper attitudes. If one once recognizes that bad temper is 
futile, that it is wasteful of emotion, and that it interferes with sane 
reasoning, he will overcome it. It is particularly valuable to think 
things through to a conclusion and to keep a sense of humor. These 
are invaluable in overcoming nervous difficulties and building up 
an optimistic view of life. 

Introspections are usually to be avoided in adolescence. When 
one thinks about himself, it is from so emotional and prejudiced a 
viewpoint that a fair judgment cannot be made. Day dreams 
may be conducive to success. They may make one ambitious and 
spur him on, if he dreams of achievements. But, if imaginary 
slights are exaggerated and dwelt upon, such thinking leads to 
mental disturbances. Social intercourse with other children, par- 
ticularly in free play, is especially desirable in order to help a 
child adjust himself in the social group in which he must live. 

A feeling of inferiority is a symptom common to a disturbed 
nervous system. When children are laughed at, or spurned, or too 
severely criticized, they lose their self-confidence and their self- 
respect. This feeling of inferiority inhibits effort and causes dis- 
satisfaction, unhappiness, and possibly failure. Responsibilities 
should be given such children. Confidence, respect, and whole- 
some consideration should be shown their efforts, so that they will 
make proper efforts toward success. Children should be able to 
take effective action when necessary. 

Self-pity and lack of confidence are also undesirable. They may 
come from trying to accomplish things that are too difficult or are 
beyond the mental ability. Talking over problems with a person 
whose judgment is valuable and worthwhile, often helps to direct 
a person's activities along the proper lines. It reduces strain and 
worry and prevents the repression of thought. 

Effects of Tobacco and Alcohol on the Nervous System. There 
is a distinction to be made between the effects of tobacco upon 


young people and adults. Many school records show that, in 
general, smokers have lower scholastic standing than non-smokers. 
The use of tobacco in early youth forms a habit that becomes 
increasingly hard to break and in many instances has harmful 
effects upon the general ability of the person. 

Tests have been made to see the effects of alcohol on mental 
and motor achievements. One of these tests showed that after 
a person takes alcohol in any form the rate of his pulse is 
increased, steadiness is decreased, coordination is lessened, and 
his ability to add is decreased. In all the tests that have been 
made, alcohol appears to reduce functional capacity. Recent 
tests show that alcohol is not a stimulant but a narcotic. The 
apparent stimulation following the taking of alcohol is due to the 
deadening of the nerve centers of control. The higher nerve 
centers of judgment and decision become dulled, resulting in irre- 
sponsibility. The memory tests which were conducted showed that 
seventy per cent less work was done when the subject was using 
alcohol. Many industrial organizations, railroads, and mercantile 
houses require their men to be total abstainers. The experience 
of these, corporations proves that alcohol interferes with efficiency 
and is directly responsible for many accidents. The investigation 
of these two drugs is still largely experimental. 


1. What is the relation of intelligence to school progress? 

2. What remediable conditions may cause failure ? 

3. What can be done with dull children ? 

4. How do you think that it is possible for psychologists to deter- 
mine the intelligence necessary for efficiency in various positions ? 

5. What precautions are necessary for keeping the nervous system 
in good condition ? 

6. What is fatigue ? How can it be overcome ? 

7. What are the objections to worries, fears, bad temper, and 
introspection ? 

8. What can be done for a person with an inferiority complex ? 


9. What is the value of play, leadership, and success to a child? 

10. Why do some people dislike their work ? Is it possible to rem- 
edy this condition? 

11. Criticize the habit of debating with oneself without coming to 
a decision. 

Supplementary Readings 

Burnham, Wm. Henry, The Normal Mind (D. Appleton and Co.). 

Gates, Arthur I., Psychology for Students of Education, Chap, xviii (The 

Macrnillan Company). 
Robinson, James Harvey, Mind in the Making (Harper Bros.). 
Terman, L. M., Intelligence of School Children (Houghton, Mifflin Co.). 
Wiggam, Albert Edward, Exploring Your Mind (D. Appleton and Co.). 



Louis Pasteur. 

His flask of nutritive fluid. 

What was one of the ancient ideas of the origin of life? How and 
by whom was the theory of spontaneous generation disproved? How 
do some scientists of to-day explain the origin of life f 

The ancient idea of the origin of life. At the time of Aristotle, 
and for many centuries following the work of this Greek teacher 
and philosopher, there was a theory, supported by scientific men, 
concerning the origin of life, and known as spontaneous generation. 
According to this theory, living things rose spontaneously from 
non-living materials. Bees were supposed to come from the dead 
bodies of young bulls; young rats could be made to appear in a 
box containing soiled rags and wheat grains ; horsehairs in water 
would turn to worms ; and mice and other animals came from the 
mud of the river Nile. Dew was supposed to give rise to insects, 
and rain would bring frogs. Instead of investigating whether 
this was the way life originated, people speculated that it must be 
true and scorned anyone who doubted it. The unbelievers were 
told to go to the Nile and see the fields swarming with mice begot 
from the mud which was deposited when the Nile overflowed its 

Experimental evidence. Francesco Redi, an Italian physician, 
(1629-1694), was one of the first persons to conduct a series of 
experiments to test, scientifically, the theory of spontaneous 





Using this simple experiment, Redi started a discussion which ended 
with the overthrow of the belief of spontaneous generation. 

generation. He had noticed that flies were usually seen about 
meat, and thought that there might be some connection between 

flies and the mag- 
gots which were 
supposed to rise 
From the meat. 
As a result of 
this observation, 
he put some meat 
in three different 
jars. One of 
these jars was 
left uncovered, 
one was covered with parchment, and the third was covered with 
a fine gauze. In the first jar, the meat spoiled; maggots and, 
later, flies appeared in the mass. In the parchment-covered jar, the 
meat putrefied, but no maggots appeared. In the gauze-covered 
jar, the meat putrefied, and flies laid eggs upon the gauze. These 
eggs produced maggots which later developed into flies. Therefore, 
Redi concluded that maggots of flies could not have originated 
from decayed meat alone, but from fertile eggs laid there by other 
flies that were attracted by the odor. No eggs were found near 
the second jar as the parchment kept the odor from escaping. 
Redi decided that life must come from preexisting life. He per- 
formed other experiments and concluded that in cases when life 
seemed to have been produced from dead matter there had always 
been the introduction of material from living organisms. 

Leeuwenhoek's contribution. After Redi's experiments, the 
question of the origin of life was again discussed. Many people 
were willing to accept the explanation that the living things they 
could see, such as rats and frogs, must originate from other living 
things. In 1687, Leeuwenhoek perfected the microscope and dis- 


covered an entirely new world of living microorganisms. He dis- 
covered bacteria and protozoa, which many investigators said were 
the organisms from which more complex organisms originated. 
By means of the microscope he was able to prove that the weevils 
found in granaries were hatched from minute eggs deposited on 
the wheat grains by winged insects. 

Needham and Spallanzani. About 1770, Needham, an English- 
man, became interested in these experiments. He boiled meat 
extract in glass flasks which he closed securely with corks. He 
thought he had killed all the life present with the boiling process. 
In every case, he found that great numbers of microorganisms 
appeared sooner or later. He decided that if life appeared, it 
must originate spontaneously. He started the spontaneous gen- 
eration controversy anew. The Abbe Spallanzani, an Italian, sus- 
pected that Needham had not been very careful in conducting his 
experiments and that germs in the air might have entered the flask. 
He repeated the same experiments, but used glass flasks that 
could be hermetically sealed in a flame while the infusion was still 
hot. No organisms appeared. Needham objected to Spallan- 
zani's experiment, saying that the prolonged heating had destroyed 
the nutritive value of the substance. Spallanzani then per- 
mitted some air to enter the glass and almost at once microscopic 
organisms appeared, showing that the nutritive qualities of the 
material were still there. 

The importance of oxygen. About this time a scientist named 
Priestley discovered oxygen and its importance to life. Scientists 
now asked whether the boiling of the closed flasks had not changed 
the oxygen so that it had lost its life-giving properties. But no 
more scientific experiments were performed until 1836, when an ex- 
periment was devised that permitted clean air to enter the culture 
medium continuously. Organisms in the air were removed by 
passing the air through a series of tubes containing substance which 
would kill all living matter. No organisms appeared in the flask. 


Many scientists were now willing to accept the fact that living 
organisms did not originate spontaneously. 

The revival of the discussion. After some years of practically 
no discussion on the subject, Pouchet, in 1859, suddenly revived the 
controversy. He believed that spontaneous generation was one 
of the means employed by nature for the production of living 
things, so he set out to prove it. He filled a bottle with boiling 
water and inverted it with the mouth of the bottle under mercury. 
Then, by means of a delivery tube, he introduced oxygen through 
the mercury into the bottle of water. The oxygen gradually dis- 
placed some of the water. By means of a pair of forceps, which 
he had first heated, he thrust some hay through the mercury into 
the bottle. The hay, too, had been carefully heated to a very high 
temperature. The hay floated in the water in the bottle, in the 
oxygen atmosphere. Microorganisms appeared in great numbers. 

Louis Pasteur enters the controversy. A French scientist, 
Louis Pasteur, thought that Pouchet had not set up his experiment 
carefully enough and that germs must have entered with the oxygen 
or hay. Pouchet asked how it was possible for air to contain so 
many germs that they developed in every organic material. He 
said the air would be misty with them. Pasteur began to wonder 
whether germs might not be more numerous in some air than in 
other air. 

In order to investigate this, Pasteur filled a number of glass 
flasks with a liquid that would easily spoil. He boiled the liquid 
and sealed the flasks while the liquid was still boiling. He opened 
some of the bottles in different places where there were people 
and dust. He then sealed the flasks again, and in all cases organ- 
isms appeared. He next went to the Alps to investigate air at an 
altitude so high that it would be free from dust. He went to the 
Mer de Glace, high up in the Alps. He opened twenty of the 
flasks that had been carefully prepared, and immediately sealed 
them again. Subsequently, microorganisms appeared in only one 


flask. Pasteur concluded that the amount of dust and germs 
in different localities must vary. In reporting this experiment 
to the French Academy of Sciences, he stated that the study 
of the germs which accompanied dust might lead to a knowledge of 
the origin of various diseases. But the conception of germs and 
disease was so vague that no attention was paid to this statement. 

While Pasteur was conducting his experiments in the Alps, 
Pouchet was testing air in Sicily, on Mt. Etna, and on the sea. He 
found microorganisms in all his air tests. Many people believed 
in the validity of Pouchet's work rather than that of Pasteur's. 
One scientific journalist wrote that Pasteur's work was too fantastic 
to be exact. 

Then Pouchet decided to repeat Pasteur's experiment. Accom- 
panied by two other scientists, he departed for the Alps with a 
number of narrow-necked flasks filled with hay infusion. At the 
foot of a glacier of the Maladetta, 3000 meters above the sea level, 
he opened four of his flasks. Then the tubes were carefully sealed. 
Microorganisms soon appeared in the flasks. Pouchet then con- 
cluded, since there was no dust at the place where he had opened 
the flasks, that air did not bring in the germs, but that they 
must arise by themselves from the organic material. 

The debate became so heated that the Academy of Sciences 
appointed a commission to examine the experiments of Pasteur 
and Pouchet. Both scientists were invited to present their experi- 
ments, but Pouchet said the weather was so cold that it might 
compromise his results. Some time later, Pasteur was invited to 
give a lecture on spontaneous generation at a scientific meeting at 
the Sorbonne. A theatrical performance could not have drawn a 
larger crowd. Every seat in the room was taken and many 
scientists and students were there. Pasteur simply and care- 
fully performed his experiments, explained them, and presented 
his conclusions. He explained to the audience that boiling 
destroyed the germs, but if air entered after the boiling, it carried 



in more germs and the organic material would then decompose and 
show numerous microorganisms. If care were taken that no 
air entered, no organisms appeared. He repeated Pouchet's first 
experiment and showed a source of probable error. In a darkened 
room, he directed a beam of light upon the apparatus and the 
audience saw that the surface of the mercury was covered with 
dust particles. Pasteur showed that when the forceps were 
plunged through the mercury, they took some of the dust particles 
with them. He then explained that the floating particles of dust 
contained living germs. Later, the Commission decided that the 
contest should be settled by one experiment. Pouchet wanted 
more. The Commission refused and gave its decision in favor of 

John Tyndall. In 1876, John Tyndall, an English physicist, 
published the results of his experiments. He had devised a very 
elaborate box or chamber which enclosed a volume of air. This 

was so regulated that any 
particles floating in the air 
would settle and be held on 
a sticky substance, such as 
glycerine, spread over the 
sides of the box. Tyndall 
passed a powerful beam of 
light through an opening 
in the box to make sure 
that no free dust particles 
were present in the air. If 
dust particles were present 
in the air, the beam of 
light would illuminate 
them. Then he applied heat to the test tubes of nutritive fluids 
that were suspended in the box. These fluids consisted of mutton 
broth, turnip broth, and fluids from other plants and animals. 

Tyndall's apparatus added further data which 
helped disprove the theory of spontaneous genera- 
tion. Identify the different parts of the apparatus 
from the description given in the text. 


The mouths of the test tubes were freely exposed to the air in 
the box. The fluids remained free from microorganisms for an 
indefinite period of time. Later, in order to check his results 
and to demonstrate that the fluids contained nutritive value, he 
removed them from the box and exposed them to the outside air. 
Microorganisms appeared. The importance of this work and the 
work of Pasteur was far reaching. Keeping dust out was the 
basis for the sterilization of wounds and surgical instruments, 
which later led to antiseptic surgery. It was, also, the basis of 
canning by heating. 

Origin of life. If life comes from life, where did the original 
life come from? Science has been unable to solve this riddle. 
One theory, popularly accepted by some scientists, is that when 
the earth cooled down, there were unusual conditions that made 
possible the combining of certain elements in the right proportion 
to form the simplest one-celled plants. From these plants, gradu- 
ally the entire plant and animal kingdoms have originated. There 
are no means of knowing whether this actually took place or not. 
The origin of living matter still remains unsolved by scientists. 

Questions and Suggestions 

1 . State the ancient idea of the origin of life. What evidence have 
you for thinking that some people still have this idea about some forms 
of life? 

2. Describe the first experiment that was made to prove the theory 
of spontaneous generation. 

3. Discuss the importance played by the microscope in the con- 

4. Discuss the experiments of Needham and Spallanzani. 

5. Of what value to scientists of this time was the discovery of 
oxygen ? 

G. Discuss the controversy of Pouchet and Pasteur. 

7. How do present-day scientists explain the origin of life? 



A moss capsule. 

Obelia forming buds. 

What is asexual reproduction? What kinds of organisms reproduce 
asexuallyf What are some of the asexual methods of reproduction? 

Only living things have the power to produce new organisms 
similar to themselves. Schleiden, Schwann, and other scientists 
showed that cells, living units of life, came only from preexisting 
cells. This process of a cell or cells producing other cells is called 
reproduction. It is a process peculiar to living organisms. Icicles, 
crystals, stalactites, and stalagmites may grow by tiny additions to 
the outside. These additions are known as accretions. After 
accretion has gone on for some time, parts may break off. This 
type of growth and division is fundamentally different from the 
growth and division that come from within a living cell. A given 
organism cannot live forever; therefore, nature has provided, by 
reproduction, a means of continuing the species. 

The necessity for division. In living cells, particles of food 
material are taken into the cell body and made into cell material, 
protoplasm, by the process of assimilation. This additional proto- 
plasm causes the cell to grow. The cell grows until it becomes so 
large that there is not enough surface to take in Sufficient food for 
the increased mass of protoplasm. By the process of dividing in 
half, two more surfaces may be obtained, through which food may 
be absorbed from the outside. After dividing, each cell again 




takes in food from the outside, grows to its maximum size, and 
then divides again. In the simpler animals and plants, after repro- 
duction, the new cells may separate and go about as single individ- 
uals or they may cling together. If they cling together, each acts 
as a separate individual independent of the other. 

Reproduction by binary fission. The simplest of all plant 
organisms belong to the Thallophyta. As previously men- 
tioned, they are distinguished by the character of having no 
division into roots, stems, and leaves. The thallophytes are 
divided into two sub-groups: the fungi — thallophytes lacking 
chlorophyll, such as bacteria, yeasts, and molds ; and the algae — 
those having chlorophyll, such as Pleurococcus and Spirogyra. 

Bacteria show little differentiation of structure. They consist 
of a mass of protoplasm with nuclear material scattered through 
the cytoplasm. They are surrounded by a thin cell wall. Bac- 
teria reproduce by splitting in half, thus forming two new indi- 
viduals. During reproduction, the nucleus elongates and divides. 
A cell wall is formed between the two nuclei, cutting the cell in 
half. Probably the division of the nucleus is always a mitotic 
division. Sometimes the newly, formed cells remain attached; 
often they separate. This type of 
reproduction is binary fission. 

Many of the algae reproduce 
much like bacteria. Pleurococcus 
is found on the shady, moist sides 
of trees, rocks, and stumps every- 
where. Each plant is a single cell 
consisting of a cell wall, cytoplasm 
and nucleus. It makes its own 
food, reaches a maximum size, and 
divides. The resulting cells either 
separate or remain in clusters. 

„. t1 „ ~ . ,. ., , Germs multiply rapidly when conditions 

Ihe cells or bpirogyra divide by are favorable. 



9.30 _ 


" "" 8 

















8f?M 16.77T.216 



binary fission. In Spirogyra, the mitotic figure is clearly seen 
when properly stained. As the cells of Spirogyra divide, they 

A yeast cell takes in food and grows a bud which enlarges and produces other buds. This 
results in a chain or group of yeast cells. 

cling together end to end and form a long filament. Each cell 
is an independent organism. Amitosis, division without a spireme, 
is very infrequent. There is doubt as to Whether amitosis is ever 
a method of reproduction in any normal and healthy cell. 

Many one-celled animals such as the Protozoa reproduce by 
fission. In the amoeba, the nucleus divides mitotically, the 
cytoplasm constricts between the two nuclei, and two new cells 
are formed. The Paramecium, too, reproduces by a like method. 
The micronucleus elongates, constricts, and divides. The 
macronucleus resembles a degenerative nucleus in that it divides 
amitotically. It frequently disintegrates and dies. Then the 
micronucleus builds a new macronucleus. As the cytoplasm 
constricts, a new mouth, groove, and gullet appear in one side of 
the organism. A new vacuole appears at the end of each new 
cell. The cytoplasm divides completely and the two new Para- 
mecin swim away from each other. 

Reproduction by budding. Another type of reproduction found 
among simple organisms is budding. 

Problem. Study of budding in yeast cells. 

Break a small part of a compressed yeast cake into a dilute solution 
of molasses. Stir and then let the mixture stand in a warm place over night. 
Mount a drop of the material under the low power and then the high power of 
the microscope. 



I. Describe the shape, color, and size of yeast cells. 

A. Note and describe the large vacuole in each cell. 

B. Describe any other structures that you see. 

II. Notice tiny protuberances on some of the cells. These are called buds. 
This process of reproducing is called budding. 

A. Compare the buds with the original cells as to size and appearance. 

B. Describe a difference between budding and binary fission. 

C. Compare the different buds in size. Account for the difference. 

D. Examine the field of the microscope carefully and see whether the 
buds always cling to the original cell or whether they separate from it. 

E. If the original cell is called the mother cell and the bud is the 
daughter cell, do you find any granddaughter cells ? Explain how you 
recognize them. 

F. There is a nucleus in the yeast cell although it may be difficult to see 
it without staining. The nucleus divides mitotically in forming the bud. 

G. Draw : 1. Yeast cells ten times larger than seen under the micro- 
scope. Label cytoplasm, vacuole, and cell wall. 2. Yeast cells budding. 
Label cell and bud. 3. A group of yeast cells' with successive buds. 

H. Compare your sketch with the diagram on page 248. 

Budding of hydra. Hydra, a small, many-celled animal, is often 
seen growing on the side of an aquarium jar. Hydra has a mouth, 
several armlike struc- 
tures called tentacles, 
a thick wall of out- 
side body cells, and a 
delicate inner layer of 
cells inclosing a body 
cavity. The tentacles 
wave about and cap- 
ture food which they 
convey to the mouth. 
When hydras are 
mounted under the 


The hydra often grows a bud and occasionally an animal is 
found with a daughter bud bearing active tentacles. 

microscope, one or more buds may be seen on the body walls. 
Each bud is a new animal in some stage of development. 

WH. FITZ. AD. BIO. — 17 



Photomicrograph of a hydra. 
Note the buds still attached to 
the original animal. 

Budding is not as common a form of reproduction as binary 
fission. Budding and binary fission are types of reproduction 
found only among the simplest of plants 
and animals. 

Reproduction by means of spore forma- 
tion. A third type of reproduction found 
among simple organisms is spore forma- 
tion. If yeast cells are subjected to an 
unfavorable condition of heat, food, or 
water, they sometimes go through another 
type of reproduction. Each yeast cell will 
develop an unusually thick wall. The 
nucleus and cytoplasm break up into three 
to eight parts. Very often only four parts are formed. Each of 
these parts is known as a spore. The spores will remain in the 
spore case, the thickened cell wall, until the surrounding condi- 
tions become favorable for them to live alone. Then the spore 
case will absorb water, burst, and the four yeast cells will come 
out. Each will feed, grow, and reproduce. This type of propa- 
gation accomplishes protection as well as reproduction. 

Due to lack of chlorophyll, yeast cells are unable to make their 
own food. They depend upon food already made. Their food 
consists of fruit juices and other sugar solutions. If molasses 
solution, preserved fruit, grape juice, or any 
other sweet food is left exposed to the air, wild 
yeast plants, in the form of spores, will settle 
on the surface and multiply rapidly. The 
yeast cells give off enzymes which attack the 
sugar, breaking it down into alcohol and car- 
bon dioxide. This process of yeast attacking 
sugar and converting it into alcohol and carbon 
dioxide is known as fermentation. Bubbles of carbon dioxide 
may be observed in fermented solutions. The test performed in 


Yeast cells often form 
a group of four spores. 
These last over an unfa- 
vorable period and at the 
proper time break from 
the spore case. Each 
spore becomes a yeast 


elementary science may be used to show that these bubbles are 
carbon dioxide. The alcohol may be recognized by the odor. 
The process of fermentation always accompanies the reproduction 
of yeast plants. Since the yeasts are dependent upon nonliving 
organic material for food, they are called saprophytes. 

Problem. Spore formation in mold. 

Place a piece of bread on several thicknesses of well-moistened filter paper 
or blotting paper on a plate. Expose the bread to the air, sprinkle it with dust, 
or infect it with mold spores. Cover with an inverted glass dish that is raised 
up on one side to admit a little air. Be sure the bread does not dry. Moisture, 
a limited amount of air, warmth, and organic material are necessary for the 
growth of molds. The hairy growth that appears on the bread is one type of 
mold, the bread mold. It takes from one to four days to grow these plants. 

Mount a minute amount of the hairy structure under the low power of the 

I. Describe the shape and color of the cells of the mold. 

A. Are there any cross walls to the cells? 

B. Do the cells branch or not? These cells are known as hyphae. 

C. The mat of cells is known as the mycelium. The threads that are 
actively feeding and growing are called the vegetative hyphae. 

II. Try to mount a piece of mold that was actually embedded in the bread. 
A. The anchoring rootlike structures are called rhizoids. By means of 

these, the mold gives out enzymes that dissolve some of the bread. The 
dissolved bread is then absorbed as food by the mold. 

I. Observe the structure of the mold and explain why it is prob- 
ably a saprophyte. 

II. Discuss the difference between the mold and Spirogyra in types 
of nutrition ? 

III. When the mold is three or four days old, note the tiny dark bodies that 
appear. Mount a bit of the mold structure, including several of these bodies, 
under the low power of the microscope. Be sure not to take too great a mass 
of material. 

A. Describe the structure of one of the small black bodies. This is a 

B. Describe the structure that holds the sporangium. This is a repro- 
ductive hypka. 

C. Locate a broken sporangium. Describe the structures escaping 



An aerial hypha develops a sporangium or fruiting body. 
This structure produces and disperses the spores. 

from .the sporangium. These are known as spores. Each little spore is 
capable of producing a new mold plant. 

D. Draw a complete and a broken sporangium. 

I. Label sporangium, spore, and reproductive hypha. 

A sporangium some- 
times forms at one end 
of the hypha. The pro- 
toplasm within this end 
breaks into a great many 
tiny structures, spores. 
When ripe, this fruiting 
body or spore case, the 
sporangium, breaks open 
and the spores scatter. 
The spores can outlast 
unfavorable conditions. During unfavorable conditions, the mold 
is in a dormant or resting stage in the spore. If it settles on food 
and there are proper conditions of moisture and warmth, then the 
spores will develop into new mold plants. The name for some molds 
is mildew. Certain of the molds, as the powdery mildew that grows 
on the lilac, live and secure their nourishment from living organisms. 
An organism that gets nourishment from a living plant or animal, 
and gives nothing in return, is a parasite. 

Problem. Study of sporangia in various 
types of molds. 

I. Let a peeled banana stand in a covered dish 
for forty-eight hours. When it shows a mold 
growth, examine it with the microscope for fruiting 
bodies or sporangia. 

II. Bring to class samples of various kinds of 
molds or mildews. Examine them under the micro- This photomicrograph shows 

.,,..,,. . not only a large sporangium, 

SCOpe for the fruiting bodies or sporangia. but certain of the spores are 

A t-w j.rt. , , » also in focus. Compare this 

A. Draw as many different types of spo- illustration ^ the diagram 

rangia as you have observed. at the t0 P ot the page. 



II molcl 


Diff erent species of molds form different types of sporan- 
gia. Compare the different sporangia in the picture. 

Amoebas and certain 
other protozoans may go 
into a resting stage simi- 
lar to spore formation, 
when conditions are un- 
favorable. This resting 
stage in a protozoan is 
called encystment. 
Spore formation is not, 
necessarily, a method of 
reproduction. It may 
be a method of protec- 
tion only. But since 
such a cell can germi- 
nate, when brought into 
favorable conditions, it 
is usually classed with 
reproduction. Spallanzani, Pasteur, and Tyndall discovered in 
their investigations of spontaneous generation that certain micro- 
organisms were harder to kill than others. It was later found 
that some are more resistant to a high temperature than others, 
and that some are spore formers and can resist unusual condi- 
tions, while others are incapable of forming spores. 

Each of the types of repro- 
duction described, namely binary 
fission, budding, and spore forma- 
tion, is really a type of cell division. 
Each of the new cells formed is 
I produced by a single organism. 
Therefore, it is called asexual 
(without sex) reproduction, in 
contrast to sexual reproduction 

Certain sponges reproduce by budding. ^ which tWO Organisms take part. 


Questions and Suggestions 

1. What is the purpose of reproduction? 

2. Discuss binary fission. 

3. Give examples of organisms that reproduce by binary fission. 

4. Discuss reproduction by budding. Illustrate in two organisms. 

5. Set up an experiment to illustrate fermentation. 

6. Discuss spore-formation in yeast ; in molds. 

7. Besides reproduction, what is another purpose of spore forma- 

8. Compare and contrast binary fission, budding, and spore forma- 

9. Compare a saprophyte and a parasite with an organism that 
makes its own food. Give examples. 

Supplementary Reading 

Atkinson, G. F., College Textbook of Botany (Henry Holt & Co.). 
Gager, C. S., General Botany (P. Blakiston's Son), chaps, xv-xxv. 
Greaves, J. E. and E. O., Elementary Bacteriology (W. B. Saunders), chap. vi. 
Holmes, S. J., General Biology (The Macmillan Co.), chap. x. 



Leaf with little plants. 

A sandworm with buds. 

What is vegetative propagation? What processes in animals may be 
comparable to vegetative propagation of plants ? 

An individual organism begins its independent life when it 
becomes separated from a preexisting individual. Roots, stems, 
and even leaves sometimes develop into new plants, although 
ordinarily their functions are for purposes of nutrition and not 
reproduction. When a portion of a plant, ordinarily used for 
nutrition, is separated and used for reproduction, the process is 
called vegetative propagation. Vegetative propagation is an asexual 
method of reproduction. Usually, only one organism contributes- 
to the propagation or continuance of the life of the organism. 
Man makes use of vegetative reproduction to produce new species 
rapidly. When the method of reproduction of a plant is devised 
by man, it is called an artificial method of propagation ; when it 
is found in nature, it is called a natural method. 

Artificial methods of vegetative propagation. Cuttings. Higher 
plants may be propagated by cutting pieces of stems from the 
plant and planting these cuttings in moist sand or water. If a 
twig is cut from a willow tree, and the cut end placed in water or 
moist soil, roots will usually develop from that end, while buds 
will develop from the other parts of the cutting. Each cutting will 
produce the missing parts and grow into a complete, independent 




A piece of stem cut from certain plants and placed 
in water or moist sand will grow roots. 

plant. Geraniums and other house plants are usually propagated 
in this way since they may be produced much more quickly from 

cuttings or slips than from 
the germination of seeds. 
Another advantage of slip- 
planting is that one is usu- 
ally sure to grow a plant true 
to the type from which the 
slip was taken. The seeds 
of plants do not always 
develop into plants exactly 
like the organisms from 
which they were gathered. 

Regeneration. • There is a 
type of propagation found 
among certain animals that 
is somewhat similar to cuttings of plants. It is possible for many 
organisms to reproduce lost parts and grow into complete individ- 
uals. The common earthworm is a good example. If a worm 
is cut through the middle, each half may develop the missing parts 
and each part may become a complete worm. Certain flat worms 
may be divided into several parts and each part will become a 
complete individual. Sponges are propagated by cutting a sponge 
into many sections and sowing the ocean floor with them. Each 
section will develop into a complete organism. The regrowth or 
reproduction of the parts of an organism which have been lost or 
destroyed is called regeneration. If some animals such as crusta- 
ceans (lobsters, crabs, shrimps) and echinoderms (starfishes, sea 
urchins, sea cucumbers) lose one of their appendages or rays, they 
are able to regenerate these parts. Sometimes a lobster is seen 
with one claw much larger than the other. This probably indi- 
cates that the smaller is a second growth, the first having been 
lost in a fight or through an accident. 



In the higher animals, including man, whole organs are not 
restored. A process similar to regeneration is evidenced, though, 
in the healing of a wound and in the knitting of a broken bone. 
An ordinary scratch or even an extensive cut often heals without 
so much as a scar, because the destroyed cells are quickly re- 
placed by new cells. The capacity of lower animals to regener- 
ate an entire individual from a portion of another individual is an 
extreme example of the same ability as is manifested in the heal- 
ing of a wound. The type of regeneration shown in the regrowth 
of destroyed tissues is known as physiological regeneration in con- 
trast with the regeneration that is a method of propagation. 

Grafting. If, under certain conditions, the freshly cut surfaces 
of two plants are brought into contact with each other, the plants 
will grow together as one. People for many ages have been using 
this knowledge for the propagation of fruit trees. A stem called 
a scion is cut from a tree and is so attached to a rooted stem called 
the stock that the cambium or growing layers of each are brought 
into close contact. The actively growing cambium cells of each 
unite the two stems. In time, food from the stock will pass 
through the ducts and nourish the scion. This is called astern 



Animals often regenerate lost parts. The lower animals, when injured, may grow back 
few or many lost organs. The simpler the animal, the greater is the power of regeneration. In 
the human body only limited regeneration takes place. 




graft. During the process of 
uniting, the two stems must be 
closely bound to prevent them 
from breaking apart. A coat of 
grafting wax protects the region 
of contact from an excessive loss 
of sap and evaporation of water, 
and from contact with spores of 
fungi. Successful grafting is ac- 
complished only between mem- 
bers of the same or closely 
related species. Stem grafting is 
commonly used in propagating 
fruit trees. 

Grafting is, also, done by 
means of buds. A bud on a strip 
of bark with its underlying cam- 
bium layer is cut from a branch 
and is inserted into the slit in the bark of the stock so that the two 
cambium tissues are in close contact. The process of binding and 
waxing is similar to that used in stem grafts. Fruits, nuts, and 
flowers are obtained more rapidly by grafting 'than by the plant- 
ing of seeds. The graft will probably always breed true to the 
scion type. Consequently, 
as in the case of propaga- 
tion by cuttings, a horticul- 
turist is sure of the result of 
the graft, if it is successful. 
Grafting is also a method of 
propagating seedless fruits. 
If a seedless fruit has been 
produced by plant breeding, 
it is propagated vegeta- 

eleft grafting 

Twigs may be grafted together in 
various ways. 

+ soion. — * sHieia. bu<wnn 


Shield budding is a type of grafting. The bud of 
the desired variety is inserted into a slit in the bark 
of the stock. It is then bound tightly to keep in 
place until healing and growth take place. 



lively by grafting. Every possible tree of the same or closely 
related species may be made use of in grafting. If a tree is found 
to produce inferior fruit, instead of uprooting it and planting new 
seeds, a scion from a tree that produces good fruit may be grafted 
on the inferior tree. If the grafting is successful, the original tree 
will, in the future, produce the 
improved variety. Varieties of 
the Old World grape have been 
grafted on the stock of the wild 
grape, and from this combination 
we have obtained the different 
types of grapes found in our 
country to-day. The roots of 
the Old World grape are easily 
injured by a root louse, but 
the roots of the wild grape are 
not affected by this insect. Be- 
sides, the wild grapes are hardy 
and are able to grow well in this 
climate. By grafting, it has been 
possible to produce grape vines 
that are immune from destruc- 
tion by the louse, and yet yield 
the desired type of grape. 

A type of grafting is fre- 
quently used by surgeons in ani- 
mals. But, here, grafting is a type of regeneration and not of re- 
production. In most cases, grafting is only used when tissues are 
severely injured. For example, if considerable skin has been de- 
stroyed by a burn, small sections of skin are removed from other 
parts of the body and grafted on the injured area. This grafted skin 
grows over the injured area and thus repairs the tissue. If a bone 
in the body is tubercular, sections of healthy bone from another 


Tongue grafting is a type commonly used. 
The important feature here, as in all grafting, 
is to bring the cambium layers of stock and 
scion together. 



Layering is a modification of cutting. It consists in 
bending down a stem and covering it with earth. Deep- 
notching or ringing the bark of the part buried usually 
hastens the rooting of the stem. 

part of the organism 
may be grafted on to the 
diseased bone. But, to 
a large extent, grafting 
of tissues, bones, and 
even organs is still in 
an experimental stage 
and has not proven suc- 
cessful in all instances. 
Natural methods of 
vegetative propagation. 
Layering , another 
method of propagation, 
often occurs without 
the assistance of man. 
In many cases the 
branches of a tree or 

brush may bend down until they come in contact with the soil. 

Sometimes they become covered with soil. If there is sufficient 

warmth and moisture in the soil, the branches will develop roots. 

Frequently, after developing roots, they break off from the tree 

and form an entirely new plant. The raspberry, with its arching 

stems, illustrates this type 

of propagation. 

Runners are branches 

that trail along the ground. 

Sometimes, the ends or 

joints of these branches 

come in direct contact with 

moist soil. Roots and, 

finally, a shoot develop at 

this point, forming a new 

plant. Strawberries, as 




When runners are found in plants, they may be used 
as an easy and rapid method of propagation. 



Underground rootlike stems or rhizomes are charac- 
teristic of some plants. As they run under the ground, 
they give off buds which form new plants. 

well as many grasses and 
weeds, are usually propa- 
gated in this way. Seeds 
of strawberries are so 
very difficult to cultivate 
that horticulturists de- 
pend entirely upon the 
runners for propagation. 
Rhizome. A common 
form of subterranean 
stem is the rhizome or 
rootstock. It is a hori- 
zontal stem running 
under the ground. As it grows beneath the soil, it sends off roots 
from its under surface, and leaf -bearing branches from its upper 
surface. The rhizome is usually somewhat thickened with food. 
Growth takes place year after year from the same rootstock which 

bears the annual scars of 
the ground stems. In the 
common ferns, the so-called 
fronds are simply large 
leaves developed directly 
from the rhizome. Blood- 
root, Solomon's-seal, wake- 
robin, lily of the valley, 
and many other spring 
flowers are propagated from 

Tubers. The potato 
plants have slender, under- 
ground stems. Certain 

Potatoes can be raised from seeds. The usual . „ . 
method of propagating potatoes, however, is to use a reglOllS 01 these Stems en- 
part of the tuber with an eye. The eye is a bud | » , « rp, 
from which the stems and roots grow. large to torm tubers. lhe 




A whole bulb and the cut section of two bulbs are 
shown. Note the short stem and the thick fleshy leaves 
arranged around the stem. 

" eyes " in the tubers are really buds. When used for propagation, 
the potato is cut so that each section has at least one " eye." 
These sections can be planted and each bud or "eye " will develop a 

root system and an aerial 
stem. Each tuber can 
form as many plants as 
it has buds or "eyes." 
Nourishment in the form 
of starch is stored in the 
tuber and feeds the grow- 
ing plant until its leaves 
are produced. Some- 
times when potatoes are 
kept in a damp cellar, the eyes absorb moisture and begin to 
develop into stems. 

Bulbs. A bulb consists of a modified under-ground stem. 
Leaves, thickened with stored foods, grow from this stem and 
closely overlap each other to form the scales of the bulb. A 
terminal bud growing from the tip of the stem is in the center 
of the scalelike leaves. If a bulb is cut, the parts of an entire 
plant may be seen. When planted, the embryo stem absorbs 
food from the inclosing thickened leaves, sprouts, and develops 
into an elongated stem bearing true leaves. As the stem 
elongates, it sends up the leaves and flower blossom above the 
ground. The true leaves manufacture more food than is needed 
and the surplus is sent down to the under-ground stem, where it 
is again stored to form another bulb. Sometimes, more than 
one bulb will be formed. Onions, tulips, and some lilies are 
examples of plants that may be propagated by bulbs. A col- 
lection of bulbs may be seen in the narcissus. Bulbs are fre- 
quently dug up from the soil so they will not freeze in winter. 
Before they are again planted, they are separated from each 
other and planted singly. 


In all the forms of propagation discussed, the continuance of 
the species is insured. Only one organism is involved in the 
process. A part of one organism propagates an entire new organ- 
ism. Consequently they are all forms of asexual reproduction. 

Questions and Suggestions 

1. What is vegetative propagation? Why is it a method of re- 
production ? 

2. Name three artificial methods of vegetative propagation. 

3. Set up an experiment to illustrate propagation by cutting. 

4. What is the value of cuttings ? 

5. Discuss regeneration. 

6. Devise an experiment to show how grafting is done. 

7. Name and describe five natural methods of vegetative propa- 

8. Discuss two methods of vegetative propagation by over-ground 

9. Discuss three methods of vegetative propagation by under- 
ground stems. 

10. Secure, and bring to class, some plants that propagate by 
layering, by runners, and by rhizomes. 

11. Plant a tuber and a bulb and observe their growth. Draw 
them in various stages of growth. 

Supplementary Readings 

Gager, C. S., General Botany (P. Blakiston's Son & Co.). 
Transeau, E. N., General Botany (World Book Co.). 



Maturation of an egg. 

Maturation of a sperm. 

What is sexf What are some different types of sexual reproduction f 

Sexual reproduction in mold. In many organisms, instead of a 
single organism developing directly from a half or a part of another 
one, two special cells from different organisms unite to form one 
cell. The cell resulting from this union develops into a new 
organism. The two cells that unite are called gametes, and the 
cell formed as a result of the union is called a zygote. The forma- 
tion of a zygote is called sexual reproduction. Certain lower plants 
reproduce both asexually and sexually. Normally, the bread mold 
reproduces by asexual spores. When growth conditions are 
unfavorable, a sexual method of reproduction may occur in this 
organism. Two threads or hyphae of mold plants will grow 
toward each other until the tips meet. A cell wall forms near the 
end of each tip, cutting off a part of the protoplasm at the end of 
each hypha. These are similar in size and appearance, and are 
known as the gametes. The intervening walls between the gametes 
are dissolved and the contents of the two cells intermingle. A 
thick wall develops around the fused material, the zygote. As the 
zygote grows the outer wall becomes black. The structure in this 
stage is called a zygospore. Under favorable conditions the zygote 
germinates, and develops into a new plant. 

When the uniting gametes of an organism are* very similar in 
size and activity, their union is -called conjugation. Therefore, a 




zygospore may be defined as a structure resulting from the conju- 
gation of similar gametes. Although the hyphae of a mold all look 
somewhat alike, there must be a physiological or cjiemical differ- 
ence between them. It has been 
observed that there are two 
types of hyphae, which have 
been named the plus and the 
minus strains. If a plus strain 
meets a minus strain, conju- 
gation will occur. It is now 
possible to isolate or to pur- 
chase plus and minus strains 
of mold spores. When these 
are planted on opposite sides 
of a slice of moistened bread, 
hyphae will grow out from each 
strain and when they meet, 
zygospores are formed. 

Sexual reproduction in Spiro- 
gyra. During sexual reproduc- 
tion in the Spirogyra, portions 
of the cell walls between the 
two filaments grow perpendic- 
ular projections and form a 
bridge. The cell walls in the 
middle of the bridge are dis- 
solved, probably by the action 
of enzymes. Then through the 
work of vacuoles the entire contents of the cell in one filament are 
moved across the bridge and fused with the protoplasm of the 
other cell. After conjugation, a thick cell wall develops around 
the fused protoplasm and the structure is known as a zygospore. 
If one cell in a filament is an active cell, that is, its contents^ pass 

WH. FITZ. AD. BIO. — 18 


Hyphae of mold plants grow toward each 
other and meet. In the area of contact, mate- 
rial from each intermingle to form a zygospore. 





through the bridge, all 
the cells in that fila- 
ment are active cells. 
If one individual in a 
filament is a passive 
cell, all other cells of 
that filament are pas- 
sive or receiving cells. 
There is more physio- 
logical differentiation 
in the Spirogyra than 
in the mold, in that 
the gametes behave 
differently. The ac- 
tive gametes may be 
compared to male gam- 
etes of higher plants and animals, the passive, or receiving gam- 
etes, to female gametes. After the zygospores are formed, the 
filament sheath breaks down, the cell walls disintegrate, and the 
zygospores fall to the bottom of the pond. They stay in a dor- 
mant condition until there is sufficient water and warmth to pro- 

There seems to be two different strains of bread mold 
called plus and minus. The hypha of unlike strains attract 
each other and zygospores are formed. 

When two threads of Spirogyra lie parallel to each other, ad- 
jacent cells may send out little tubes which meet. The cross 
walls in the tubes become dissolved, leaving an unobstructed 
bridge. The entire contents of one cell (active gamete) will pass 
over and mingle with the contents of the other cell (passive gam- 
ete). Fusion takes place and a zygospore is formed. If one cell 

in a filament has a moving gamete, the contents of all the cells of that filament behave in 

a similar way. 



Each of the cells which fuse during conjugation is 
known as a gamete. When very nearly alike they are 
called isogametes. Conjugation is the result of the 
fusion of part or all of the cell contents of isogametes. 
The result of the union is a zygospore. / 

mote their germination. Then each zygospore absorbs water, 
breaks the zygospore case, and forms a new filament as a result 
of binary fission. There like or isogojnetes 
is enough stored food in 
the zygospore to start the 
germination and sustain 
life until the filament can 
make its own food. 

Sexual reproduction in 
Paramecium. Paramecia 
ordinarily reproduce asex- 

ually by binary fission. Occasionally, sexual reproduction takes 
place. Two cells lie next to and in contact with each other. 
At the point of contact the cell membranes dissolve. Various 
complicated changes take place in the nuclei of the two animals. 
The macronucleus in each breaks up and disintegrates. The 
micronuclei go through a number of divisions and finally one 
fragment of each micronucleus passes over and unites with a 
fragment of the micronucleus in the opposite cell. After this 
mutual exchange and fusion of micronuclear material, the two 
Paramecia separate, and the micronucleus 
of each goes through further complicated 
divisions, which result in the formation of 
both a micronucleus and a macronucleus. 
The conjugation of the Paramecia seems 
to bring about a renewed vigor. In cer- 
tain species conjugation may occur once in 
every two or three hundred generations, 

a photomicrograph showing although these same species may live a very 
the conjugation of Paramecia. i ong timej providing conditions are favor- 
able, without ever reproducing sexually. 

Certain recent experiments have shown that the environment 
affects the vitality of the Paramecium. By removing wastes and 



The photomicrograph of a mold culture 
which shows several zygospores. 

by keeping proper food present, thousands of generations have 
been produced from a single healthy individual of a certain species. 

Under these conditions, conjuga- 
tion has not taken place between 
any two animals, but certain in- 
ternal changes occurred which 
were observed and described. 

Sexual reproduction in higher 
plants and animals. In the sexual 
method of reproduction of the 
Spirogyra, the entire cell acts as 
the gamete. In the Paramecium, 
simply a part of the micronucleus 
acts as the gamete, but like-sized 
portions of the micronucleus unite. When gametes are similar they 
are known as isogametes or like gametes. In most higher plants 
and animals, certain specialized organs produce cells that form 
gametes. There are two kinds of gametes. One, a very small 
cell usually equipped with a motile tail, is called the microgam- 
ete or the sperm cell. The other type of reproductive cell is the 
receiving or passive cell. It is larger and is 
called the macrogamete or egg. It usually 
stores food particles called yolk granules. 
When the egg is ripe, a sperm may penetrate 
the egg. The nucleus of the sperm fuses 
with the nucleus of the egg. This process 
is called fertilization. The cell formed by 
the union of the egg and sperm cell is 
known as a zygote. 

Maturation. Every species of an organ- 
ism has a constant number of chromosomes. 
The number is always the same for that species. During fertili- 
zation, when two cells unite, the number of chromosomes would 

Photomicrograph of filaments 
of Spirogyra showing conjuga- 
tion and zygospores. 



egg + ®perm * fertile egg 
macrogoroetef microganKfce,* wgbte, 

Fertilization is the union of dissimilar gametes ; 
the union results in a zygote or a fertilized egg. 

double were it not for certain changes which occur in the de- 
velopment of the egg and sperm. These changes are called mat- 
uration or the ripening of tlie 
gametes. The cells that are to 
produce the germ cells or gam- 
etes are the primary sex cells. 
They have the same number of 
chromosomes as the somatic or 
body cells. When ready to ma- 
ture, the sex cells split by a process much like mitosis, but the chro- 
mosomes do not split lengthwise. Instead of splitting evenly, 
one half the total number of unsplit chromosomes goes into one 
daughter cell and one half goes into the other. This is the part 
of the ripening or maturation process called reduction division. 

The number of chromo- 
somes is reduced one 
half. After this, each of 
these cells again divides, 
mitotically. Thus from 
every primary sex cell, 
cells are produced, each 
of which has • half the 
original number of chro- 
mosomes. If» the pri- 
mary sex cell had eight 
chromosomes, each 
gamete would have half 
this number or four chro- 
mosomes. The produc- 
tion of the sperms by 
maturation of the pri- 
mary sex cells is called 
spermatogenesis ; the 




-„ The primary sex cells of the fruit fly have eight chro- 
mosomes. During the ripening process, reduction divi- 
sion takes place; the resulting cells have one half the 
original number, in this case four chromosomes. Each 
of these cells then divides, mitotically forming the sex 
cells. From each primary male sex cell there forms four 
sperms, all of which can function. Each primary female 
sex cell gives rise to one egg and three reduced cells 
known as polar cells. The egg has most of the yolk and 
is generally the only one of the female sex cells to function 
as a gamete. One sperm unites with a mature egg in the 
process of fertilization. 


production of the mature eggs is called oogenesis. All of the 
spermatozoons or sperms of a species are of the same size and 
structure. All may function. Each of them has a tail-like 
structure of cytoplasm called the flagellum. By means of the fla- 

gellum the sperms are 
able to move about. 
Oogenesis is essentially 
the same as spermato- 

Many sperms of animals may swim about the mature egg. o>pnp«ji«i Onp la rap ppII 

One sperm penetrates the cell membrane of the egg and 5 C11CS1 °- vuciaigctcii 

carries, in this case, four chromosomes. These are added jg ^g real functioning 

to the reduced number in the nucleus of the mature egg. & 

The union of sperm and egg with the restoring of the original gamete, Called the ma- 
number of eight chromosomes is fertilization. 

ture egg. It contains 
the food supply or yolk. In the process of maturation of the egg, 
three minute cells known as polar bodies are thrown off. 

Fertilization. After the maturation process, the gametes 
formed from the primary sex cells are ready for union or fertiliza- 
tion. The sperm is always in a moist environment and by means 
of its flagellum swims to the egg. In some eggs there is a small 
opening in the membrane called the micropyle. Through this 
opening one sperm enters. When an egg lacks the micropyle, a 
sperm penetrates the plasma membrane. The head of the sperm 
contains the nucleus. The flagellum or tail of the sperm is usually 
left outside of the egg. After a sperm nucleus enters the egg, a 
chemical change takes place within the cell membrane. This 
permanently seals the egg so that no more sperms can enter. 
The nucleus of the egg and of the sperm fuse. The entrance of 
the sperm restores the original number of chromosomes in the 
egg cell. Mitosis of the fertilized egg then takes place. It differs 
from typical mitosis in that half the number of chromosomes 
came from the sperm and half came from the egg. The chromo- 
somes are said to be paternal and maternal in origin. Immediately, 
mitotic division or cleavage takes place and two cells are formed, 
each with the same number of chromosomes, as the species 



to which the parents be- 
longed. From here on the 
cells cleave or split again 
and again by mitosis until 
enough cells are formed to 
take on the shape of the 
plant or animal embryo. 
The yolk in the egg sup- 
plies food for the rapidly 
dividing cells. Fertiliza- 
tion produces a variety of 
characters by combining 
chromosomes from differ- 
ent individuals. This re- 

Spring and summer aphids or plant 
lice are wingless females which pro- 
duce young, parthenogenetically, e very 
10 to 20 days. In the autumn, males 
are produced, mating occurs, and fer- 
tilized eggs are laid which last over the 
winter and hatch into females the fol- 
lowing spring. 

The parthenogenetic frogs produced experimentally 
hy Jacques Loeb resembled normal frogs in their ap- 

suits in the possibility of slight or great 
differences among offspring. 

Parthenogenesis. It has been stated 
that the entrance of. a sperm into an 
egg stimulates a chemical change in the 
membrane which seals the micropyle, 
and stimulates the egg to go through 
repeated divisions. The late Jacques 
Loeb, formerly at the Rockefeller Insti- 
tute, carried on a series of experiments 
to investigate the nature of the fertili- 
zation process. He pricked the eggs 
of sea urchins with an electric needle 
and found that this brought about a 
membrane activity and the egg began 
to cleave. He next found that certain 
chemicals caused the same results. 
This process of the development of the 
egg without the entrance of a sperm 


is known as parthenogenesis. Loeb succeeded in developing, par- 
thenogenetically, frogs' eggs. Several reached the tadpole stage. 
A few grew to be nearly adult in appearance and then died. 
Their development was incomplete. Parthenogenetically devel- 
oped organisms may have only half the number of chromosomes 
common to the species, since no sperm chromosomes are present. 
The process has never been performed, experimentally, in any 
organism higher than the frog. It sometimes occurs in nature 
in certain of the insects and certain worms. 

Questions and Suggestions 

1. What is the difference between sexual and asexual reproduc- 

2. Discuss sexual reproduction in the mold ; in the Spirogyra. 

3. State a difference between conjugation in mold and Spirogyra. 

4. Discuss sexual reproduction in Paramecium. 

5. What is the value of sexual reproduction in the life history of 
the Paramecium. 

6. Compare fertilization with conjugation. 

7. Discuss spermatogenesis ; oogenesis. 

8. What is the purpose of maturation ? 

9. State two cellular activities of the egg that always follow the 
entrance of sperm. 

10. State two differences between an unfertilized and a fertilized 

1 1 . What is parthenogenesis ? Discuss some experiments that have 
been carried on in parthenogenesis. 

Supplementary Reading 

Atkinson, G. F., A College Textbook of Botany (Henry Holt& Co.). * 

Gager, C. S., General Botany (P. Blakiston's Son & Co.). 

Holmes, S. J., Ah Introduction to General Biology (Harcourt, Brace & Co.). 





Insect pollination. 

Wind pollination. 

How are new plants formed? What is the function of a seed and 
of the fruit f What are some different types of fruits f 

A flowering plant consists of the nutritive organs, the roots, 
stems and leaves, and the reproductive organs, which are found 
in the flower. The reproductive organs in the flower produce 
specialized cells, gametes, which function in sexual reproduction. 

Problem.' Study of the tulip. 

If the tulip is not in season, the gladiolus, sedum, or any perfect flower may- 
be used. (The flower was probably studied in elementary science, so certain 
facts learned at that time are not emphasized in this exercise.) 

I. Remove the three outer sepals and the three petals found within them. 

A. What is the relation of the position of these parts to the organs found 
in the center of the flower ? 

B. What are the functions of the sepals and petals? 

II. Locate the organs in the center of the flower. Why are they called 
essential organs ? 

A. The single enlarged structure found in the center of the flower is the 
pistil. The upper end comprises the stigma. The lower part of the 
swollen stalk is the ovary. 

B. The structures with spear-shaped heads arranged around the pistil 
are the stamens. The heads of the stamens, the anthers, produce the pollen. 
How does the pollen escape from the anthers ? 

C. Draw a pistil. Label stigma and ovary. Draw a stamen. Label 
anther and pollen. 




III. Shake some pollen from the anther on to a glass slide. Mount under 
the microscope. 

A. How many cells make up each pollen grain? 
'■ ... B. Describe the shape, color, and structure of pollen. 

C. Draw and label several pollen grains enlarged ten times. 

IV. Cut a thin cross section of the ovary of the pistil. Examine it with a 
hand lens. 

A. The seedlike structures are the ovules. Note that the ovules are 
attached to the ovary wall and are not loose in the ovary. The part of 
the ovary wall to which the ovules are attached is called the placenta. 

V. Place an ovule on a glass slide. Cover it with a cover glass and crush it 
by carefully pressing down with the cover glass. 

A . Does an ovule consist of one or more cells ? 

B. Note a central structure. This is the embryo sac containing the egg 

C. Draw the outline of an ovule showing the position of the embryo 

Structure of the flower. The flower consists of a calyx made up 
of sepals and a corolla made up of petals. While the essential 

organs are ripen^ 
ing, they are pro- 
tected from rain, 
insects, and certain 
mechanical injuries 
by the tightly en- 
folding calyx and 
corolla. The whole 
structure com- 
prises the bud. As 
the essential organs 
ripen, the calyx 
and corolla unfold 

The essential organs for the reproduction of higher plants are the 
stamens and pistils. Accessory organs are the sepals and petals, and expose the 
The sepals enfold the entire flower, forming a bud. Thus the . 

organs are protected while they are ripening. The petals are fre- matured pistils and 
quently showy and attract insects. This may result in pollination. 
The stamens produce pollen and the pistil produces ovules. Stamens. 





Problem. What effect has a sugar solution on 
pollen grains t 

Make up cane sugar solutions of thirty-five per cent, 
ten per cent, and three per cent. Take three hanging- 
drop glass slides and on each one lay a cover glass from 
the center of which hangs a drop of sugar solution con-, 
taining some pollen. Use a different sugar solution for 
each slide. Seal the cover slip air tight by means of 
vaseline. (Petri dishes or Syracuse watch crystals may, 
also, be used.) Different pollen requires different 
concentrations of sugar solution in order to grow. A 
three-per-cent sugar solution is usually needed for tulip, 
narcissus, and onion ; fifteen per cent for sweet pea and 
nasturtium. Let the preparations stand for one or two 
days. Then mount under the microscope. 

I. Describe the shape of the pollen grains when first 
produced by the anther. 

II. Describe what has happened to the grains. 
A. These outgrowths are called pollen tubes. 

^ B. Describe the food for the pollen tubes which 
you have grown. 

III. Carefully crush the tip of a ripe stigma on a 
glass slide and mount under the microscope. 

A. Do you find any pollen grains here? 
1. How did they get on the stigma? 

B. Do any pollen grains show pollen tubes ? 

1. In which direction are they growing? 

2. Where must the germinating pollen tubes 
obtain their food ? 

IV. Draw and label a germinating pollen grain. 


Production of the male gamete. Pollen is 
produced in the anther of the stamen. Certain 
cells in the anther go through a maturing 
process in which reduction division takes place. 
Mature pollen nuclei contain one half the number of chromosomes 
characteristic of the other cells of that particular plant. When 

A pollen grain has two 
nuclei, one a tube nu- 
cleus, the other a gener- 
ative nucleus. As the 
pollen grain forms the 
pollen tube, male gam- 
etes (the sperm nuclei) 
are produced from the 
generative nucleus. 



mature, the ripe anther of the stamen splits and scatters the 
pollen. Agencies, such as wind, insects, or water, may assist in 

Complicated nuclear divisions in the embryo sac of the ovule of a plant result in the formation 
of eight nuclei, of which one is an egg nucleus and two are polar nuclei. The two polar nuclei lie 
near the center of the cell. The egg nucleus is the female gamete. 

scattering the pollen. When pollen reaches the stigma of the 
pistil, it may be caught and held by hairy outgrowths particularly 
adapted for that purpose. The stigma then secretes certain 
nutrient materials which the pollen absorbs. After this pollina- 
tion*, the pollen grain germinates by sending out a slender thread- 
like tube. The pollen tube 
grows down through the pistil 
and penetrates the ovule 
through an opening called the 
micropyle. As it grows, cer- 
tain nuclear divisions take 
place, which produce two sperm 
nuclei. The sperm nuclei with 
their reduced number of chro- 
mosomes are the male gametes 
of the plant. 
* Production of the female 

A photomicrograph of a part of an ovule show- -n i_ 1 j.i~ 

ing the nuclei in the embryo sac. Compare it gamete. J^aCIl OVUie in the 
with the diagram at the top of the page. » j , i_ 

ovary is lormed as the out- 
growth of a few cells from the ovary wall. One of the cells in 
the interior of the young ovule appears larger and richer in 



protoplasm than the other cells. It divides, and, in the division, 
reduces the number of chromosomes by one half. There are a 
number of complicated divisions that follow. Ultimately, an egg 

& poller & 





r e g£ cell 

A longitudinal section of a pistil shows pollen grains germinating through the pistil in the form 
of tubes. One tube is shown penetrating the micropyle of the ovule. The pollen tubes carries 
the sperm cells to the embryo sac of the ovule. 

nucleus and two polar nuclei are produced among other nuclei 
found in the embryo sac. The egg nucleus with its reduced 
number of chromosomes is the female gamete of the plant. 

Fertilization. When the end of the pollen tube gets to the 
embryo sac, the wall of the pollen tube and the wall of the 
embryo sac are dissolved and one of the two sperm nuclei unites 
with the egg cell nucleus. The two polar nuclei fuse and the 
second sperm nucleus sometimes unites with them. This completes 



m*cl«u* "\ xy6 ote 

In the process of fertilization in a flower a 
sperm nucleus unites with an egg cell nucleus 
to form the embryo of the future plant. The 
other sperm nucleus unites with a pair of 
nuclei, the polar nuclei. This latter union re- 
sults in the endosperm nucleus which divides 
and, in time, forms the food supply for the 
embryo. Double fertilization is characteristic 
of flowering plants. 

the process of fertilization. The 
union of the sperm and egg nu- 
clei forms the one-celled embryo 
which develops into a tiny 
plant. The union of the other 
sperm nucleus and the polar 
nuclei forms the cell that starts 
the endosperm which is the food 
supply of the tiny plant. This 
double fertilization results in the 
future plant and its food supply. 
Formation of the seed and 
fruit. There are ducts going 
from the plant through the 

.remains of stigma 
ana ♦st^-Ie^- 


placenta of the ovary to the ovule. 

Food passes through these ducts, * 

which nourishes, and effects the I 

rapid division or cleavage of cells I 

in the tiny embryo in the ovule. 1 

At the same time, the endosperm \ 
tissue of the ovule grows rapidly and 
stores the future food supply for the 
embryo. As the embryo develops 

into a many-celled structure, dif- : 

ferentiation of the cells sets in and | 

the first root or hvvOCOtyL the first After fertilization takes place in a 

J vr v > J flower, the petals, stamens, and frequently 

bud Or plumule, and the Seed leaves * h e stigmas of the pistil dry and generally 

fall off. The embryo and endosperm de- 

Or Cotyledons are formed. The en- veloo and the ovule coats grow to accom- 

, ii i • modate the increased size of the seeds, 

dosperm develops at the Same time, The pod with its contents is the fruit. 





In the grains, the endosperm is a well-developed, localized, and 
easily identified structure ; in seeds such as beans, peas, and many 
nuts, the cotyledons possess 
the food supply for the devel- 
oping plant. 

While the embryo and endo- 
sperm are developing, the ovule 
coats absorb food from the 
ducts and develop into seed 
coats. The ripened ovule and 
its contents constitute the seed. 
The ovary wall grows to accom- 
modate the developing seeds 
and forms the fruit. The fruit 
protects the seeds until they 
are completely developed. 
Fruits are frequently adapted 
to disperse the ripe seeds. 
These seeds escape from the 
fruit, and the embryos they con- 
tain will develop into new 
plants, if they fall on moist 
soil of proper temperature. 
The fruit is a ripened ovary and its contents, together with any 
other part of the plant that has ripened with it. 

When the bean seed is planted, it absorbs water, and sends a 
little arched shoot, the hypocotyl, into the ground. The lower 
seed or radicle forms the root system. As the upper part or 
true hypocotyl straightens out, it brings the plumule above the 
ground. This forms the stem and leaves. The cotyledons feed 
the tiny plant until its leaves are able to make sufficient food to 
carry on the life process. The cotyledons may either remain under- 
ground or be lifted into the air by the growth of the hypocotyl. 


Given the proper conditions of moisture and 
warmth, a new plant will develop from the embryo 
in the seed. Which of the organs of the plants is 
developed from the hypocotyl ? 


Questions and Suggestions 

1. Name the parts of a flower and give the function of each. 

2. What do we mean by self- and cross-pollination ? What are 
some agents of' cross-pollination ? 

3. Will the pollen of a daisy germinate on a rose ? How do you 

4. Give the history of the pollen grain from the time it is pro- 
duced until it functions. 

5. Give the history of an ovule until fertilization takes place. 

6. Discuss the fertilization of an ovule. 

7. , How many seeds can possibly be produced in any plant ? 

8. What three processes are necessary for the formation of- a seed ? 

9. Discuss the development of a seed and a fruit. 

10. Discuss the adaptations of the following plants for dispersing 
their seeds : maple, elm, thistle, Bidens, pea, apple. 

11. Give examples of seeds or fruits dispersed by (a) wind; 
(6) animals. 

12. Cut a longitudinal section of some fruit (apple, cucumber, water- 
melon, pea). Draw and label seed, seed stalk, placenta, ovary wall. 

13. Plant a bean seed. When it appears above ground, uproot it 
and draw. Label hypocotyl, plumule, and cotyledons. 



N. Y. Zoological Soc. 
The buck has antlers. 

N. Y. Zo'dlogical Soc. 
A doe with her fawn. 

7* the reproduction of an animal similar to that of a plant f Do all 
animals reproduce in the same way? IJow does an animal develop 
from the fertilized egg f How long does the development take f 

Seeds and eggs. The common form of propagation for higher 
plants is through the formation of seeds, and for higher animals, 
through the production of fertile eggs. Most seeds are capable of 
sprouting even after remaining at rest for a long time, sometimes 
after many years. The germs in the seeds are destroyed, how- 
ever, if the seeds become very wet and then dry again. 

The eggs of chickens and other birds are well known. The eggs 
of fish and frogs are somewhat similar to those of birds, although 
they are found in the water. Eggs of butterflies may frequently 
be seen on plants. Those of water animals usually die if they 
become dry. Birds' eggs have to be kept warm if they are to in- 
cubate and to hatch. Those of insects may lie dormant over the 
winter and develop in the spring. In general, eggs need more care 
than seeds. In the case of many animals, the eggs must develop 
soon after they are formed or they will die. They cannot live in 
a dormant form for an indeterminate period of time as seeds can. 

Secondary sexual characters. In the lowest animals, it is often 
quite impossible to distinguish the individuals that produce male 

WH. FITZ. AD. BIO. — 19 281 



gametes from those that produce female gametes. Among the 
frogs, fishes, and other lower animals, there is little external mor- 
phological difference in sex, but the higher species of animals show 
external differences. In addition to the structures that are directly 
related to producing and discharging gametes, distinct character- 
istics are found in other parts of the body. The males of many 
species of birds can be easily recognized by the crests on the heads 
and spurs on the legs. The male birds are usually more gayly 
colored and have sweeter songs than the female birds. 

Among many mammals (animals that are warm-blooded, 
covered with hair, and suckle their young), there are usually differ- 
ences in horns, size of body, habits, voice, temperament, and in- 
terests. Contrast the male reindeer with the doe. The male is a 
huge animal with tremendously large antlers. He is a vicious 
fighter and protects the doe. She lacks antlers, is proportion- 
ately small and slender, and usually depends upon the male for 
protection. The differences just noted are called the secondary 
sexual characters of reindeers. 

Spawning of frogs. Fertilization takes place in animals in a 
way very similar to plants. The gametes mature and are then 
brought together in a way peculiar to the organism. Different 

The lioness and lion show interesting secondary sexual characters. 

shaggy mane of the lion. 

N. Y. ZoOiogicul Soc. 
Note the huge head and 



species of frogs reach 
maturity in different 
periods of time. At 
maturity, the female 
frog lays fifty or a 
hundred eggs,, ova, in 
the water. Each ovum 
consists of a tiny cell 
surrounded by yolk or 
food which is covered 
with a gelatinous 
coating. The adult 
male frog discharges 
sperms into the water. 
These sperms are mo- 
tile, swimming by 
means of tiny tails. 
If a sperm comes in 
contact with an egg, 

it penetrates the egg The cow, placid in disposition, is easily distinguished from 

the excitable and frequently dangerous bull. 

membrane, and the 

nuclei of the egg and sperm unite in the fertilization process. If the 
eggs are not fertilized, they soon die and disintegrate. If sperms 
do not reach eggs, they, too, are wasted. The fertilization of 
the frog's eggs is external to the body and takes place in the 
water. This differs from the plant where fertilization was in- 
ternal, taking place in the ovary of the pistil. After fertilization, 
the gelatinous sheaths of the frog's eggs absorb water and swell. 
This mass of foamy material insures some degree of protection 
against enemies. Fish or other frogs cannot readily swallow this 
huge mass of gelatinous eggs. 

Fish spawn in a way very similar to frogs. They usually go to 
quiet, shallow waters for spawning, although a few species of 



I Q.-he«a, 
" nucleus 


Fish seldom show secondary sex characters. 
The sex organs are the ovaries in the female, and 
the testes in the male. The ovary produces nu- 
merous ova, each of which contains a yolk and a 
nucleus. The testis produces numerous sperms, 
each of which has a nucleus, a head, and a 
motile tail. 

river fish spawn in the ocean. So powerful is the urge to spawn 
in natural spawning grounds, that the salmons will leap falls or 
artificial barriers in their efforts to reach quiet water on their way 
from the deep sea. Many die of exhaustion on their way if they 
meet too many obstacles. Those that surmount the barriers usu- 
ally die soon after spawning. 

Production of eggs. Certain organs of the frog are specialized 
for the production of gametes. In the female, the two ovaries 
secrete hundreds of tiny ova. The ovaries may be compared to 
the ovaries or pistils of flowers which produce egg cells. Ovaries 
are common to all females in the animal kingdom. The ova of 
the frog go through a maturation process in which the number of 
chromosomes is reduced one half. This process results in the 
production of mature gametes. The mature ova reach the body 
cavity of the frog and then pass through the tubes called oviducts 
into the cloaca. They leave the cloaca by means of an open- 
ing at the posterior end of the female frog's body and pass into 
the surrounding water. Ova are characterized by their compara- 



tively large size, due to the yolk in them, and the fact that they 
are incapable of independent motion. 

Production of sperms. The pair of organs that secretes the 
male gametes or sperms is the testes. The sperms, too, in the 
maturation process lose half their chromosomes. By means of 
tubes the mature sperms of the frog pass from the testes into the 
cloaca and out of the body. These sperms are known as milt. 
Each sperm is a single cell consisting largely of a nucleus. The 
cytoplasm is drawn out to form a tail. By means of the tail 
lashing back and forward, the sperm swims in the water. (Prob- 
ably a chemical attraction draws the sperm to the egg.) The 
nuclei of the sperm and egg fuse in the fertilization process, form- 
ing a fertilized egg cell, the one-celled embryo. In this process 
the original number of chromosomes is restored. 

The entrance of the sperm into the egg effects the initial devel- 
opment of the egg as well as brings about variation by combining 
the chromosomes from two parents. * Each fertilized egg contains 
one-half maternal and one-half paternal chromosomes. 

Development of the frog. The fertilized egg or embryo absorbs 
food from the yolk. It grows and divides mitotically to form a 
two-celled stage. These 
two cells feed, grow, !$¥&*• 

and divide to form a sy 

jour-celled stage. Mi- // 

totic divisions con- 
tinue, forming various 
many-celled stages 
called cleavage stages. 
Finally, the solid mass 

Ot Cells, the morula, p rimaryse xcells are formed early in the life of an organism, 

becomes arranged in They contain the same number of chromosomes, 2x, as body 

& t cells. In the maturing of the sex cells to form sperms and 

the form of a single- eggs, the chromosomes become reduced to half the number, 

f x. When the sperm unites with the egg to form the zygote, 

layered hollow ball of the 2x number is again restored. 



cells known as the blastula. The blastula pushes in just as a rubber 
ball may be dented in by pushing on one side. A double-layered, 

fertile egg 2-celIecL -4-celIeU 




la cellecl 


of gastrula 




two layered 

The embryo begins as a single fertilized egg. This divides to form two, then four, and cleav- 
age continues until a great many cells are formed. Gradually differentiation sets in and special- 
ized structures may be recognized. Thus the various organs of the organism develop. 

cup-shaped structure known as the gastrula is thus formed. The 
embryo is now two-layered. The outer layer is the ectoderm, the in- 
ner layer the endoderm. A mid- 
dle layer, the mesoderm, soon 



fertile eg£ 




/ | V 

ectdcLerm mesoderm endoderm, 
epidermis muscles a.i£estiv<, 

central excretory ,r- A 

nervous oy^tieni/ «ver ana. 
system ^ nccas Pancreas 


The fertile egg, by repeated divisions and certain 
changes, becomes the gastrula with its three pri- 
mary germ layers. Further differentiation and de- 
velopment goes on and the organ systems arise. 

appears between the ectoderm 
and the endoderm. The folded 
edges of the gastrula grow 
toward each other, forming a 
tiny mouth. Marked differ- 
entiation now starts and forms 
the characteristic tadpole. 
The skin and nervous system 
are formed from the ectoderm. 
The digestive and respiratory 
systems are formed from the 
endoderm. The excretory, re- 
productive, muscular, skeletal, 
and blood systems form from the mesoderm. During this develop- 
ment the yolk is entirely absorbed by the actively dividing cells- 



Life history of the frog. The little tadpole then hatches from 
the gelatinous egg. For the first two or, three days, it remains 
attached to grass by 
a sucker-like mouth. 
Then it begins to 
feed on algae and 
other vegetable 
matter. When first 
hatched, it has ex- 
ternal gills, which 
grow out into long, 
branching tufts. 
Later, four pairs of 
internal gills are 
formed and the ex- 
ternal gills are ab- 
sorbed. The hind 
limbs soon appear ; 
later, the fore limbs 
develop. The tail 
then decreases in size 
and is gradually ab- 
sorbed. The gills, 
too, are absorbed, 
and lungs are formed 
to take their place. 
The two-chambered 
heart of the tadpole becomes the three-chambered heart of the frog. 
Finally the form resembling that of the adult frog is acquired. 

Reproduction of other animals. The reproduction of all higher 
animals is similar to the reproduction of the frog. All females 
have ovaries producing eggs, and males have spermaries or testes 
producing sperms. The sperms fertilize the eggs and thereby 

N. Y. Zoological Soc. 
The frog first hatches from the egg in the form of a tadpole. 
Gradual changes take place which transform it into the adult 
frog. This change of body form is called metamorphosis. 



cause the formation of embryos. Sperm cells must be kept moist 
in order to function. In the case of frogs and fish, fertilization is 

external and the water keeps the cells 
moist. In the case of animals that do 
not live in the water, such as insects, 
birds, or mammals, the egg cell is re- 
tained within the body of the female, 
and the union of the egg and sperm is 
internal. Thus the danger of the gam- 
etes drying is averted. The embryo 
develops outside of the body when the 
fertilization is external. The water 
also keeps the developing embryo 
moist. When the fertilization is inter- 
nal, the embryo may partially develop 
or may completely develop within the 
body of the female. For example, the 
eggs of the insects start developing 
within the female, but later they are de- 
posited in the ground or on plants and 
the development continues there. 

Amer. Museum of Natural History r 

In the birds, the original egg cell ^^___ __^^ ^Vl©ll 

and yolk become surrounded by 
other materials during the passage 
down the oviduct. It becomes sur- 
rounded by a coating of albumen, 
the white of the egg, which is se- 
creted by the glands of the oviduct. 
A lime coating which forms the shell 
is then secreted around the whole 

In the case of birds, 


A section through a chicken's egg shows the tmy em- 

the embryo Starts an in- bryo attached to the yolk. Surrounding the yolk is the 

, , , albumen which protects the embryo from shock. Two 

temal development, thin membranes within the shell form an air chamber at 

The fertilized egg re- oneemL 

ceives a huge deposit of yolk, then albumen is spread around it, 

and finally it is enveloped in a hard shell of lime. The yolk 




£l£e ©f 

A photomicrograph of a fertile egg that has been incubated for 
two days. Cell differentiation and specialization have taken 
place to the extent that the brain, heart, and blood vessels can 
be recognized. 

and albumen serve as food for the developing embryo and at 
the same time keep it moist. The shell permits air to enter, 
but prevents the ^*~~~' VolW 

evaporation of ^.^mfiCW^^f. 

moisture. Then 
the mother bird 
lays the egg, and 
the development 
of the embryo con- 
tinues in the egg, 
but external to the 
mother's body. 

In mammals, for 
example the rabbit, 
the entire develop- 
ment is internal. 
When the embryo 
is completely developed into a young animal, very much like the 
adult, it is born. The word " birth " is used to describe the process 

of the little individual coming 
forth after complete internal de- 
velopment. This is in contrast 
with hatching, which is the com- 
ing forth of an animal from an 
egg. During its internal devel- 
opment, the mammalian embryo 
is kept moist and warm within 
the body of the mother. It is 
fed by absorbing food from blood 
vessels which pass through the 
placenta of the mother organism. 
There is a similarity in function between the placenta of flow- 
ering plants and the placenta of mammals. They both are the 

The unborn mammal is suspended in the 
uterus by the umbilical cord. Surrounding 
fluids serve as protection against shock. Food 
for development is absorbed by osmosis 
through the placenta. 



2 days 

5 days 

10 days 

15 days 

20 days 

As development of the egg takes place, more and 
more differentiation occurs. The yolk serves as the 
food for the developing organism. First the cir- 
culating system may be recognized, later the head, 
limbs, and other organs. When the animal is com- 
pletely developed, it pecks its way out of its shell. 


parts of the mother organism, through which the developing em- 
bryos are fed. In the case of many plants, ducts and sieve tubes 
pass through the placenta and through the seed stalk and thus 
carry nourishment to the seed. In the case of mammals, the 
blood vessels of the embryo extend into the placenta through 
a cordlike structure somewhat similar to the seed stalk. 

Questions and Suggestions 

1. Name three differences between seeds and eggs. 

2. Describe the spawning of frogs. 

3. Give the following facts concerning the reproduction of the frog : 
reproductive organs, the names of reproductive gametes, where ferti- 
lization takes place (use the word external or internal), where the 
organism develops, and the food of the developing embryo. 

4. Discuss the complete development of the frog embryo. 

5. Name the germ layers of the embryo and state the organs devel- 
oping from each layer. 

6. Using the outline headings given in question 3, fill in the out- 
line for a flower, bird, and mammal. 

Supplementary Readings 

Atwood, Wm. H., and Heiss, Elwood D., Educational Biology (P. Blakiston's 

Son & Co.). 
Haupt, Arthur W., Fundamentals of Biology (McGraw-Hill Book Co.). 
Holmes, S. J., General Biology (Harcourt, Brace & Co.). 
Jewett, F. G., The Next Generation (Ginn and Co.). 
Scott, George G., The Science of Biology (T. Y. Crowell Co.). 
Wiggam, A. E., Fruit of the Family Tree (Bobbs-Merrill Co.). 



The cat takes care of its 

The young kangaroo in its 
mother's pouch. 

What proportion of offspring lives to maturity? What is the relation 
of the period of adolescence to length of life? Do all animals take 
care of their young f What animals show the greatest parental in- 
stinct f 

We have already learned that all plants and animals start life as 
single cells. In some species this single cell is a spore, in others 
a zygospore, and in still others a fertile egg. Whether the crea- 
ture is a Paramecium or an elephant, it started life as a single cell. 

The offspring of simple organisms. When an amoeba, a bac- 
terium, or any other one-celled organism divides into two new 
cells, the production of the new individuals marks the disap- 
pearance of the parent. It is impossible for the daughter cell and 
the mother cell to exist at the same time. Yet, it would not be true 
to say that the mother cell dies, for the protoplasm of which it 
consisted continues to live in the two new daughter cells. Each 
of the young amoebas is quite as capable of taking care of itself 
as is the older individual from which each came. Except for the 
growth in the comparatively short time between one cell division 
and the next, which in the case of some organisms would be only 
about twenty minutes, the young individual is in every way like 
the full-grown individual. There is, probably, some difference in 
size, however. 



Among the lowest plants and animals that produce spores or 
encysted cells, the new individual usually has a cell wall or coat 
that is somewhat thickened. This is a means of protection against 
drought, mechanical injury, or perhaps against the digestive juices 
of some animal that might ingest it. The cell also contains a tiny 
drop of oil or some other excess of food material that will sustain life 
until the protoplasm is able to obtain food through its own activi- 
ties. Such cells are usually produced in large numbers and are de- 
posited in every current of water and air. Only a very small propor- 
tion of such reproductive cells ever starts a new life. It is very largely 
a matter of chance which one will and which one will not mature. 
For example, mold spores are scattered by the bursting of the spo- 
rangium. They are found practically everywhere ; but only those 
that fall upon food in a favorable environment will develop. 

Infancy among seed plants. In the seed-bearing plants, each 
generation receives from the preceding one a great deal more 
than a quantity of protoplasm. The gametes are produced in 
proportionately small numbers, compared to the reproductive 
elements of seedless plants. The female gametes especially are 
very few, only one to each ovule. Then there is a great variety 
of structures whose function is to make fertilization possible and 
probable. For example, the display of the flower by means of 
the showy corolla and fragrance will attract the insects that are 
in search of nectar. In taking the nectar, the insects will be- 
come covered with pollen which they will later, accidentally, 
transfer to other flowers. The position and character of the 
stigma of each flower show special adaptations to catch pollen, 
and to aid and effect the formation of the pollen tube. All these 
are parts of the equipment of the parent plants, which aid in the 
process of fertilization. 

The fertilized ovum or zygote is retained within the ovule. It 
is supplied with nourishment which the young embryo uses up 
in developing. The growth of the embryo goes on to a certain 



Spanish nettle 

acorn. blacictoerry- 

— ,._- stem 


. ., danSLelioa larkspur- * ^.w^t^ 
clematis 4 ocf>ple 


Fruits and seeds are frequently adapted for dispersal from the parent plant. Winglike and 
feathery structures are adaptations for wind dispersal ; barbs and sweet fleshy parts are adapta- 
tions for dispersal by animals. 

point and then stops. A surplus of nourishment, in the form 
of endosperm or cotyledons, may be stored about the young em- 
bryo. Additional protective covers generally grow about the seed. 
All of these processes and structures are clearly related to pro- 
tecting the young plant and supplying it with nourishment that 
it can use until it develops the leaves which make its own food. 
The seed cover, or the fruit, often possesses a variety of struc- 
tures such as wings, stickers, fleshy pulp, or down, which aid the 
young seed to travel some distance from the parent plant. These 
structures are also the result of parental activity, and they con- 
tribute to conditions that make for the favorable growth of the 
young plant. If the young plants were to grow too close to the 
parent plant, they might not secure sufficient sunlight for starch 
manufacture nor enough minerals from the soil for protein man- 



ufacture. The seed is protected while. within the fruit. It has 
been supplied with food which it can use long after it has left the 
ovary, and it has been supplied by the parent plant with some 
adaptation in order to get away to a more favorable environment. 
Infancy among lower animals. Frogs, fish, and other water 
animals usually produce large numbers of eggs and sperms and 
discharge these into the surrounding water. Probably many thou- 
sand more sperms than eggs are produced. Even though a large 
proportion of the eggs may become fertilized, most of the sperms 
die as they greatly outnumber the eggs. Probably only a small 
proportion of the fertilized eggs ever get far beyond the earliest 
stages of development They are frequently devoured by animals 
in the water. Because fertilization takes place in the water and 
the embryos develop externally, a great majority of the young 
die or are destroyed. 

H. Armstrong Roberts 
The mother hen watches over, shelters, and helps the chicks gather food. 



There is very little care of the young among the lower animals 
such as frogs and fishes. In many cases the parent dies before 

the egg has had time to hatch. 
The fertilized eggs are usually 
left unprotected. In an occasional 
species there is some evidence of 
what may be called parental care. 
For example, in some fishes, the 
parent may find a protected spot, 
as under a rock, and lay a mass 
of eggs. The salmon and other 
fish that spend part of their lives, 
in salt water and part in fresh 
water, migrate many miles up large 
rivers and deposit eggs in shallow 
water far from their natural en- 
emies. Yet, of the one or two 
million eggs laid by each female, 
only a very few will ever reach 
maturity. Among the crustaceans 
(lobsters, crabs, shrimps) the female sometimes produces a sticky 
fluid about the eggs. As the eggs come out of the body and be- 
come fertilized, they are at- _ ., - . - - - 
tached to the swimmerets on 
the abdomen of the female 
and remain there until the 
embryos are ready to hatch. 
Among the mollusks (oysters 
and clams) the fertilized eggs 
remain within the cavity of 
the mother's mantle and so 

are protected by the shell until the young hatch and are able to 

Museum of Natural History 

The female lobster carries the eggs while 
they are developing. Special hairs attached 
to the appendages of the abdomen secrete 
a sticky substance which holds the eggs in 
place. This secures protection. 

The female crayfish not only carries her eggs 
attached to the swimmerets, but by straightening 
her abdomen and waving the swimmerets brings 
the eggs in contact with a supply of oxygen. 



Infancy among insects. There is a wide range of egg-laying 
habits among insects. Some kinds of insects leave the eggs almost 
anywhere. Others lay the 
eggs in a material that is 
likely to furnish food for 
the young as soon as the 
eggs hatch. The grasshop- 
per lays her eggs in the 
ground and never sees them 
again. The butterfly lays 
her eggs on a leaf and, 
shortly afterwards, dies. 
The fly deposits eggs in de- 
caying meat or other or- 
ganic matter so that food 

. 1/11 The butterfly usually lays her eggs on the food that 

IS present IOr the fly larvae wUl be used by the tiny larvae. When the little cater- 

i . i -. j £ j pillars emerge from the eggs, they begin to eat the 

Wnicn natcn OUt 01 the eggS. leaves upon which they hatched. 

The elaborate preparation for the laying of eggs of ants, bees, 

wasps, and termites is remark- 
able. The solitary wasps show 
great industry and ingenuity in 
building their nests, in catching 
caterpillars or spiders, in treating 
■-x&*J$j&S£^*c the prey to prevent decay, and 

in packing these victims into a 
nest with the eggs. The adults 
die or fly away shortly after 

In the autumn, the female grasshopper lays completing Such a nest, and they 
fertilized eggs in a hole she digs in the ground. . 

These eggs stay in the ground during the winter, never have a chance to See their 
The rays from the sun of the late spring warm _ . , . 

the earth and incubate the eggs. Small newly Onspnng. In the bee COlony, 

hatched grasshoppers crawl from the earth. , , i i l 

the young are remarkably pro- 
tected. The eggs are laid in certain cells of the hive. When the 
egg hatches into a minute, footless grub or larva, it is fed for the 

WH. FITZ. AD. BIO. — 20 



first few days on rich food produced in the stomach of certain of 
the worker bees that act as nurses. Later, they are fed with a 

The digger wasp fills her nest with spiders stung in such a way as to paralyze and preserve 
them. An egg is laid on each spider; when the larva hatches it is well supplied with food. 

mixture of pollen and honey. Certain of the worker bees act as 
soldiers to guard the hive. 

Infancy among birds. Among the birds, the new individual 
receives a large amount of protection and food for a very long 
period. After fertilization, which takes place inside the mother, 
the egg immediately starts to develop. The yolk and albumen 
represent large food supplies, and the shell is an effective protec- 
tion. After the egg is laid in a specially made nest, the develop- 
ing embryo is kept warm by the parent's body. This is known 
as incubation. It makes possible a safe and rapid development. 

Both the parents of many species of birds take part in the 
nest-building, in protecting the nest, and in incubating the eggs. 
When the young of some species come out of the eggs, they are 
fully developed and very much like the adult. The young chick, 
for example, begins to walk and to pick up food particles almost 



immediately. Among other birds, such as robins and eagles, the 
young birds are quite helpless. ■ The feathers have not developed, 
the eyes are closed, and the nestlings are not able to feed them- 
selves. The parents fly about gathering insects, fish, lambs, or 
whatever it is that constitutes their food. They bring this food 
home to the nestlings. They protect them from other animals 
and teach them, in due time, how to fly and get food for them- 
selves. Only when the young are strong enough to fly and forage 
for themselves are they put out of the nest. Birds lay compara- 
tively few eggs because, due to internal fertilization and parental 
care, each egg produced is almost sure to develop into a young 
animal. Birds usually lay one egg at a time, and when the number 
that is usual for the particular variety 
of bird is reached, the parents start 
to incubate the eggs. Compare this 
number, one to sixteen, with the mil- 
lions of eggs produced by the salmon 
and the lack of parental care after 
the salmon eggs are laid and sprayed 
with milt. 

Infancy among mammals. The 
embryo of a mammal is protected, by 
the mother's body, a longer time than 
that of any other animal. During 
this period, development goes on, 
and at birth, the young is easily rec- 
ognizable as belonging to a particular 
species. The embryos of different 
species take varying lengths of time 
to develop. The rabbit develops 
from the fertile egg in three weeks and 

then is born ; the human baby needs about nine months ; and the 
elephant about two years. This shows remarkably rapid develop- 

Care of young is often shown by 
birds. The tailor bird weaves an elab- 
orate hanging nest in which the eggs 
are hatched and the young cared for. 
Both the mother and father birds brood 
over them. One forages for food while 
the other keeps the nestlings warm. 



N. Y. Zoological Soc. 

N. Y. Zoological Soc. 

ment of cells considering the fact that 
each" animal originated as a single 
fertilized cell. 
The kangaroo and the other mar- 
supials, pouch animals, give birth to the young while these are 
still poorly developed. The babies crawl into the pouch on the 
mother's abdomen. The skin lining this pouch contains glands 
that secrete a milky fluid by means of which the young kanga- 
roos feed. All female mammals have well-developed milk glands 
and normally suckle their young for a long or short period of time. 
Some mammals are able to stand or walk immediately after 
birth. This is true of the calf and of grazing animals generally. 
Among other species, the new-born young is completely helpless. 
The kitten does not open its eyes for several days. The human 

N. Y. Zoological Soc. 

Care of young reaches its heights among the mammals. 



N. Y. Zoological Soc. 

N. Y. Zoological Soc. 

baby does not begin to walk for a 
year or more. Generally, we „find 
that the higher the species the longer 
the infant depends on its parents for 
protection and nourishment. 

Infancy in man. In man, protection of the young is shown in 
the highest degree. Not only is there a long period of dependence 
of the baby upon the nourishment obtained from the mother's 
body before birth, but there is a long period of suckling after birth. 
The greatest care and protection are given the young during its 
infancy and childhood. As communities become more prosperous, 
there is a tendency on the part of the parent to postpone for each 
child the assumption of individual responsibilities. 

Among the different races of mankind, and even among different 
peoples of the same race, there is a great deal of variation with 

N. Y. Zoological Soc 
Note the length of infancy given in the table on the following page. 




Growing Period 

Length of Life 


Elephant (Asiatic or 
Indian) .... 

Full grown but not fully 
mature at 25 years. 
Full vigor and strength 

. at 35. 

70 to 80 years. 


Camel - . 

4 to 6 years. 

20, very rarely 35 to 40. 


Horse . . . 

3 to 4 years. 

18 to 30 years ; very 
rarely to 40 years. 


Cattle . . . 

3 to 4 years. 

14 to 20 years. 


Sheep . . . 

1 to 2 years. 

6 to 10 years. 


Pig ... . 

1 to 2 years. 

6 to 12 years. 


Dog. . . . 

• 2 years. 

12 years. 


Norway Rat 


14 months. 

3 years. 


Cat . . . . 

1 to 2 years. 

12 years. 


Lion . 

3 to 4 years. 

12 to 20 years. 


Man . . . 

20 to 25 years. 

65 to 75 years. 

Compiled by Dr. C. V. Noback, New York Zoological Park. 

regard to the prolongation of infancy. In general, development is 
found to be more rapid in warm countries than it is in colder 
regions. For this reason maturity, in practically all forms, is 
reached at an earlier age among peoples in the tropics and semi- 
tropics than among those who live in temperate and colder coun- 
tries. This, however, cannot be accepted without admitting an 


exception. The Eskimos, for example, mature, in general, at an 
earlier age than the English. There are, no doubt, other factors 


m W \ 

v W *?- Jfl 1 

1 Fk r^k 


(Madame Le Brun and her daughter.) 

All through the ages, artists, in their works of art, have expressed mother 
love and the dependence of children. 

than climate that influence development and maturity. It is 
probable that nutrition has an influence. There is also another 
side to be considered, for rapid development or early maturing is, 
generally, connected with relatively shortened duration of life. 
The average length of life and the proportional number of people 
of advanced age are usually greater in those communities that 
give the children a longer period in which to develop, protect them 
more completely from various dangers, and look after their needs 
more thoroughly. 

Development of parenthood. Among the simplest organisms, 
there is no period of life corresponding to parenthood. At a certain 


phase in the organism's growth, it divides into two parts, In the 
act of reproduction, it ends its own existence. Among the higher 
organisms, especially birds and mammals, reproduction of new 
individuals is generally repeated for a long or short period of 
years. A considerable portion of the individual's activities has 
to do with preparing for and caring for the young. In man- 
kind, parenthood often makes a greater demand upon the individ- 
ual than just making a living. On the other hand, the increased 
activities of adults for the young make possible for each genera- 
tion a better preparation and a richer equipment for life. So 
much that concerns and so much that is of value to humans lie 
beyond the problems of making a living in the material sense. 

Questions and Suggestions 

1. What are the advantages to a species in producing eggs or 
seeds ? What disadvantages ? 

2. Explain the necessity for such a tremendously large egg produc- 
tion among fish as compared with the small production among birds. 

3. How can an organism make provision for offspring that it can 
never see or know ? 

4. What are some of the advantages of prolonged infancy ? What 
are some disadvantages ? 

5. How may animals that look after their young benefit from such 
activities ? 

6. How can plants be said to take care of their young ? 

7. What are some of the dangers from which the young of plants 
must be protected ? 

8. What are some of the dangers from which the young of animals 
must be protected ? 

9. Discuss whether or not a kitten's development can be hurried 
by forcing its eyes open ? 

10. Discuss whether there is any way of hastening or slowing up the 
development of a plant or an animal ? 

11. Make a special report on the breeding habits of the stickle- 
back or some other nest-building fish. 

12. Give a report on the migrations and breeding habits of the 
salmon or of the eel. 

13. Give a report on the breeding habits of the " obstetrical toad " 
and compare these with the breeding habits of common toads. 


14. Report on the migrations and nest-building of the egret, cow- 
bird, or some particular species of bird to show the relation of these 
activities to the protection and welfare of the young. 

15. Give a library report on the care of their young by ants. 

16. Give a library report on the care of their young by spiders. 

17. Describe the domestic life of some carnivorous mammals. 

18. Report on the community life of the beaver with special regard 
to the care of the young. 

19. Report on the social life of some anthropoid. 

Supplementary Readings 

Guyer, Michael F., Being Well Born; An Introduction to Heredity and Eugenics 

(Bobbs-Merrill Co.). 
Haupt, A. W., Fundamentals of Biology (McGraw-Hill Book Co.). 
Holmes, S. J., General Biology (Harcourt, Brace and Co.). 
Jewett, Mrs. F., The Next Generation (Ginn and Co.). 





f ii 

m "1 

Br- ** 

■ 1 


1L ^. 

Museum of Natural History 
Turtle Eggs. 

Museum of Natural History 
Dinosaur Eggs. 

What characters can be inherited f What is the relation of environ- 
ment to heredity •? Can a person consciously influence his inherit- 
ance? What constitutes good environment? 

Variety in protoplasm. The fact that the living matter of all 
plants and animals is protoplasm, has already been discussed. All 
protoplasm is alike in certain of the elements that compose it ; it 
is alike in its growth by assimilation, its sensitiveness to stimula- 
tions, and its response to these stimulations. Yet protoplasm of 
one species is different from that of another. The protoplasm 
of a squash seed, for example, develops only into a squash vine 
and never into a rosebush, never into a canary. The protoplasm 
of a wren's egg develops into a wren, never into a willow tree nor 
a wolf. These differences are thought to be located in certain 
parts of the chromosomes called genes. These genes are the real 
carriers of hereditary traits. By a gene is meant the part or unit 
factor of the chromosome, which is supposed to represent an 
hereditary character. The development of the organism depends 
largely upon the character-determiners of the genes. 

A many-celled organism grows by the individual cells dividing 
mitotically. In this mitotic division, each chromosome splits into 
two parts exactly alike. Hence, the chromosomes in all cells 




derived from one cell will be alike. The squash seed contains 
protoplasm that is a combination of the protoplasm of the parent 
plants. The protoplasm in the fertile egg of a frog is a part 
and a continuation of the protoplasm of the parents of the frog. 
Each kind of protoplasm continues to be much the same, genera- 
tion after generation. 

There is no difficulty in recognizing maple trees, because all 
maple trees resemble each other. Bean plants resemble bean 
plants. Elephants resemble elephants. All the individuals of a 
species are much alike. Yet no two individuals are ever exactly 
alike. We might call by name and know several hundreds of the 

(in Animals and Plants) 

Common Name 

Scientific Name 


In Body 

In Gam- 


Sycandra raphanus 





Hydra fusca 





Lumbricus herculeus 




Snail, fresh water 

Paludina vivipara 





Cambarus virilis 




Malarial mosquito 

Anopheles punctipennis 




House mosquito 

Culex pipiens 




House fly 

Musca domestica 





Asterias vulgaris 





Rana catesbiana 





Gallus domesticus 





Felis catus 


35 and 36 

17 and 18 


Canis familiaris 


21 and 22 

10 and 11 


Equus caballus 





Macacus rhesus 





Homo sapiens 





Spirogyra neglecta 





Sphagnum squarrosium 




Bracken fern 

Pteris aquilina 





Pinus sylvestris 





Pisum sativum 





Triticum vulgare 





Zea mays 




♦Reprinted by permission from Wilson: The Cell in Development and Heredity (1925) by 
The Macmillan Co. 



pupils of our school. Scientists distinguish, in a like manner, thou- 
sands of individuals of one species of a plant or animal. These 

International News Service 
Variations in the heads of birds. All the birds in 
the picture may be descendants of the same original 
ancestor. Compare these with others that you know. 

are all enough alike to be classed as insects, pigeons, or dahlia 
plants ; but each is different in some way from all the others. 

The problems of these likenesses and differences are the problems 
of heredity. The study of heredity includes a study of all the 
various characteristics in the offspring that are more or less similar 
to those characters of the ancestors. 

Environment influencing development. Individuals of the 
same species may differ because all do not have exactly the same 
conditions during their early development. Differences in tem- 
perature, in the relative amount of moisture, in the character of 
weather, or of food may cause plants to be stunted or slow to 
flower in one region when compared with the similar plants of 
another region. A more abundant supply of mineral salts, or more 
sunshine at certain periods, may produce plants that are some- 
what better developed than others grown from the seeds of the 
same parent plant. Every farm, every roadside, and every city lot 
furnish examples of plants that have thrived better or worse than 
their neighbors, because of variations in their environments. 

Temperature, moisture, light, and food are some of the factors 
that influence the development of animals as well as of plants. 
The male of the European bullfinch has a bright red breast ; the 
female is entirely brown. If the male bird is fed on hempseed, its 
plumage changes to a dull color similar to the female. Among honey- 


bees, a given egg may develop either into a worker or into a queen. 
This development depends upon the nourishment that the larva 
receives. It is thought by some investigators that the kind of food 
(honey or pollen) may cause the differentiation in the growing larva. 
Others think that when a larva is given large amounts of foods, it 
becomes a queen ; if a small amount of food, it becomes a worker. 

Many abnormal forms result from a variety of unfavorable con- 
ditions during development. This is true in human beings as well 
as in other species. Even where the results are not abnormal, 
inequalities of environment bring about differences among individ- 
uals of the same species. For example, lack of Vitamin D in the 
diet results in bone deformities. Lack of iodine may give rise 
to cretins. Too much food is likely to make people fat. 

Trees may become distorted by the wind. Plants grown in 
poorly-lighted places show an irregular development as the result 
of a one-sided illumination. Well-fed cows give more milk than 
poorly-fed cows. The lizards and spiders of Mammoth Cave, 
Kentucky, are colorless. Exposure to sunlight is thought to 
increase the amount of pigment in the human skin. One who has 
learned to swim behaves differently in the water from one who 
has not learned to swim. A trained horse runs faster than an 
untrained horse of the same parentage. A child who has re- 
covered from measles does not get the disease a second time 
when exposed to the infection. One can become accustomed to 
cold weather or to rainy climate. One can become skillful in 
some art or game as a result of practice; or his muscles can 
become weak after a period of disease or disuse. 

Where the differences between two individuals result from 
differences in outward conditions, or from environment, the prac- 
tical problem is to find out how to treat plants or animals so as to 
get the desired results. Will one kind of fertilizer or mineral salts 
result in more cotton per acre ? Will one kind of food produce more 
milk per cow? If so, an adjustment can be made so that the 



Japanese spaniel 


French poodle 


organism in question will benefit. Will one 
system of training make all individuals musi- 
cal, or quick at figures, or skillful in ath- 
letics ? If so, and if it is desirable, the system 
should be investigated and applied to all 

All of these examples, and others which 
they may suggest, are proof that plants and 
animals are influenced by what happens to 
them. These differences that depend upon 
the environment are known as variations. 
Because they affect the body cells of the 
organisms and not the germ cells they are 
also called somatic (body) variations. They 
affect the individual without affecting, to any 
extent, the offspring of that individual. 

Ancestry influences development. The 
careful farmer or animal raiser has learned 
to select the seeds for his planting, or the 
animals which he is to use for breeding. 
Large seeds are more valuable than small 
seeds, especially when a seed crop, such as 
beans or peas, is desired. A healthy cow 
that gives a relatively large amount of milk 
is a more promising mother for good calves 
than a cow that yields only a small quantity 



English setter 
All dogs probably originated 



of milk. The ability to produce a large 
quantity of milk is a trait transmitted 
from parent to offspring. If the farmer 
is interested in eggs for market, he 
selects hens that lay over 200 eggs a 
year, and uses these eggs for hatching 
purposes. These offspring, with a few 
exceptions, are good egg-layers. This 
trait, too, seems to be an hereditary one. 
For centuries, those engaged in plant 
and animal industries have selected the 
best individuals and the best seeds for 
continuing or improving their stock. 

Certain differences are found among 
cotton plants and corn plants, among 
cows and horses, among human beings, 
and, in fact, among all organisms that 
seem to have nothing to do with the 
kind of treatment they get. Some cot- 
ton plants produce long fibers and 
others short fibers, because they come 
from certain stock. They belong to a 
particular breed. Some calves become • 
Holstein cows and others become Jersey 
cows, no matter how they are fed. 

English bulldog 

Scotch terrier 



St. Bernard 
from the same ancestor. 


American fox hound 




1.5;; WHITE 




0.0 T STAR 







33.0-J- V ^oN IL " 33.0-j-S 

13.0- -SABLE 


S6.5,; ^FORKED 

65.0- -CLEFT 





25.3 ,5EPIA 
25.8-- HAIRY 

42.0 :L SCARLET 

59.0+ GLASS 

63.5- -DELTA 

65. S 


In the same incubator, under like conditions of moisture and 
temperature, some eggs hatch into Rhode Island Reds and some 

into Plymouth Rocks. 
One horse is said to in- 
herit a definite coat color, 
a certain shape, or the 
ability to run rapidly or 
to pull heavy loads. 
These characters are part 
of his breed. The John- 
son children are known 
to be tall and the Brown 
children are short, al- 
though they all seem to 
be given good food and 
care. They inherit their 
stature. In addition to 
anything in the environ- 
ment, which may influ- 
ence the qualities or 
characteristics of indi- 
viduals, there is some- 
thing with which the 
individual is born. Some- 
thing that influences his 
development and makes 
him different from others 
that live in the same environment. The characters that are 
inherent in the individual are known as germinal variations. They 
are a part of the ancestry because they are in the genes of the 
chromosomes in the fertilized cell. They can be transmitted from 
parent to offspring because they are a part of the germ plasm in the 
egg and sperm. 

70.0: r LOBE 
73.5" -CURVED 

88.0- -HUMPY 



U/-- 95.7' 


101. 0-t M1NUTE-G 


86 .5- ROUGH 


After Morgan 
Through careful experimentation, definite parts of 
chromosomes in the fruit fly have been found to be re- 
lated to definite structures. Scientists have mapped on 
the chromosomes of the fruit fly, the location of the genes 
which carry certain definite characters. 


How the genes behave is a problem of heredity. Experience 
has shown, that as a result of selection it is possible not only to 
maintain the quality of the stock, but also to improve it, up to a 
certain point. Wherever selection is neglected, the cultivated 
plants or domestic animals deteriorate in quality. They deteri- 
orate whenever the food or any living condition is neglected. 
The rule of the successful breeder is to select animals or plants 
showing the best ancestry. Then he should provide the best con- 
ditions for their healthy growth and development. 

Effect of environment on ancestral traits.' An unborn child may 
be influenced by conditions prevailing in either parent. Malnu- 
trition or serious ill-health on the part of the mother has an injurious 
effect on the offspring. Severe shock or grief, worry, nervous 
exhaustion, the influence of a very few diseases, lead, mercury, or 
alcohol poisons in the blood or tissues may act detrimentally on 
the unborn offspring. The effect of these conditions or materials 
is to interrupt the proper nutrition of the offspring, directly poison 
it, or, by generating toxins in the mother, poison the developing 
embryo. Disease-toxins affect unborn children to such an extent 
as to sometimes cause malformations, arrested development, 
instabilities of the nervous system, general physical or mental 
weaknesses, or even death before birth. The children of inebriates 
comprise a striking proportion of criminals, imbeciles, and those 
with predispositions toward certain diseases. All of these effects 
are environmental effects, not inherited effects. The character of 
the environment of the child before and after birth is a factor 
of great importance in the development of the child. 

Many prospective mothers think they can develop musical 
ability in a child by studying and playing music before the child 
is born. Or they hope they may produce beauty in the child by 
long contemplation of a picture of a beautiful child. The expla- 
nation frequently given for birthmarks is that the mother ate 
many strawberries or tomatoes before the child was born or she was 

WH. FITZ. AD. BIO. — 21 



Very similar twin girls. 

1 •» 1 



9 4 i» 


/rcf ra^ Chidnoff 
A recent photograph of the same identical twins. It is 
very difficult to distinguish one from the other. 

frightened by a fire. If the 
birthmark has hair growing on 
it, the explanation given is that 
a mouse frightened the mother 
before the child was born. 
Structural changes cannot be 
produced in a child by mater- 
nal impressions or mental ex- 
periences of the mother/ The 
physiological explanation of 
birthmarks is that a number of 
small blood vessels of the 
skin of a new-born infant 
have remained dilated in a 
particular spot. This is a' 
somatic, not a germinal 

The characters com- 
bined in the chromosomes 
during the union of the 
sperm and egg are the 
characters that will de- 
velop in the child. If 
musical ability is in one of 
the genes, it will be pres- 
ent in that of the off- 
spring. If not, no amount 
of practice on the part of 
the parent will develop the 
talent. The only struc- 
tural changes made in the 
offspring are those that 
can be affected by good 



or poor nutrition Or toxic materials of one sort or another. Only 
by affecting germ cells can the character of the offspring be con- 
trolled or changed. Recently, it has been demonstrated that in- 
ternal secretions circulating in the blood of the parent may affect 
the germ cells. Thus, if a mother's thyroid is overactive and too 
much thyroxin circulates in the blood, the germ cell may be 
affected in such a way that abnormalities in the developing off- 
spring are frequently brought about. 

Differences among offspring. It has long been known that 
certain characteristics or qualities reappear in successive genera- 
tions. Why do not all the characteristics of the parents reappear ? 
If each new individual were merely a portion of an older individual, 
it could readily be seen how the characters would continue from one 
generation to the next. When plants are propagated by cuttings 
or by grafts, the plants thus produced remain rather uniform. 
Where reproduction is sexual, two germ cells, the gametes, come 
from different sources. Each germ cell carries many qual- 
ities that are characteristic of the protoplasm of each parent. 
These qualities reappear with a certain degree of probability and in 
relationship after the two germ cells have united. Each individual 
resembles both parents, but, necessarily, also differs from both 

When two coins are tossed a great number of times, two tails turn up 25% of the times, two heads 
turn up 25% of the times and one head and one tail turn up 50% of the time. This occurrence 
is called the law of chance. In the few matchings shown in the diagram, the result would prob- 
ably not be as near the 25, 50, 25 ratio as is pictured. This illustrates the law of chance (page 317). 

parents. A child may have brown eyes like the mother's and curly 
hair like the father's. Offspring of the same parents also differ 







When peas are rolled down an inclined plane through a 
small opening against nails, they line up in pens in a very 
definite order. When this experiment is performed, a 
sorting out, known as a normal distribution, occurs. Few 
peas are found in the end pens, many in the center. This 
illustrates the law of chance, discussed on p. 317. 

from each other. Some are tall and some are short, some are 
blue-eyed and some are brown-eyed. This will be explained later. 

We have learned that 
a process called matura- 
tion or ripening occurs 
in the development of 
mature germ cells in the 
parent organism. This 
maturation of the germ 
cells accounts for the 
differences among off- 
spring. Chromosomes 
are thought to possess 
combinations of char- 
acter-determiners called 
genes. These genes are 
found to be in pairs in the primary sex cells. During the matu- 
ration process, reduction takes place. In reduction, one member 
of each pair goes to a given germ cell. Consequently, each germ 
cell has one half the number of chromosomes found in the pri- 
mary sex cell. If the primary sex cell had a pair of character- 
determiners for eye color, one of this pair carries blue and the 
other brown, the chromosome containing the gene for blue eyes 
would go to one germ cell and the chromosome containing the 
gene for brown eyes would go to another germ cell. A primary 
sex cell may have two characters Tor a particular trait, but a germ 
cell only has one and is pure in regard to any particular trait. 
Consequently, the same organism may produce germ cells with 
unlike characters. The sperm cells of the male are not identical ; 
eggs, too, have different character-determiners or genes in them. 
When the sperm and egg meet in the process of fertilization, the 
characters of the fertilized egg depend upon the characters in the 
genes in the combined chromosomes of both the sperm and egg. 


These combine according to the law of chance. Combinations of 
a pair of characters follow a definite proportion. 

Problem. How may the law of chance be demonstrated f 

I. Put in a jar one hundred black beans and one hundred white beans of 
the same size. Mix the beans thoroughly. Without looking, take out two 
beans at a time. 

A. Score the number of times two black beans, two white beans, and 
one black and one white bean are taken out. 

B. At least one hundred pairs should be taken out before the scores 
are summarized. 

C. State the proportion of two black to a combination of one white 
and one black, and to two white. 

II. Toss two coins at least one hundred times before totaling your scores. 

A. Score the number of times two tails appear. 

B. Score the number of times two heads appear. • 

C. Score the number of times one tail and one head appear. 

D. State the proportion of two heads to a combination of one head 
and one tail, and to two tails. 

III. When it is purely chance that controls the meeting of members of a 
pair of characters, the proportion resembles that obtained with the beans and 
coins. In order to get a proportion, the experiment should be carried on a large 
number of times. 

Questions and Suggestions 

1. In what structures of germ cells are characters of organisms 
located ? 

2. What is meant by heredity ? 

3. What effect has environment on development ? Give examples. 

4. What effect has ancestry on development ? Give examples. 

5. What effect has environment on ancestral traits ? 

6. Account for differences among offspring. 

7. How can the best offspring be obtained ? 

8. Discuss the law of chance. Describe an experiment to illustrate 

9. How does the law of chance operate in the fertilization of an 
egg by sperm ? 


Gregor Mendel 

Thomas Hunt Morgan 

What are Mendel's laws of inheritance f How were they formulated f 
Do these laws of inheritance hold true for all plants and animals f 

It has been found that truly heritable traits or characteristics 
of an individual are comparatively independent of each other and 
may be inherited independently. These characters are called 
unit characters. If the members of a pair of unit characters meet 
in an offspring, each member retains its identity and each char- 
acter of the pair may be separated in subsequent generations. The 
following illustration is an example of the behavior of a pair of unit 

Incomplete dominance. There are two distinct kinds of Anda- 
lusian fowls, one having white feathers splashed with black ; and 
the other, black feathers. The black fowls are known as pure black 
because, for generations, their ancestors have been black, have 
mated, and have given rise to only black descendants. The 
splashed-white fowls are known as pure white; their ancestors 
were white, they bred with white, and have always produced white 
offspring. A fowl from each group was selected as a parent. 
They were mated, fertile eggs were laid and incubated, and the 
outcome of the experiment awaited. Would the chickens be black, 
or white, or a mixture of the two colors ? Although the experi- 
ment was repeated several times, the results were always the same. 



All the young chicks were a queer mixture of mottled black and 
white which is known as blue. They were mixtures and not pure 
bred like their parents. When the members of a pair of widely 
different unit characters, in this example, black and white feathers, 
meet in an offspring, the offspring is called a hybrid. Evidently, 
neither the black nor the white character could mask or dominate 
the other, and a blending took place. The blending of a pair of 
characters is called incomplete dominance. 

Next, the investigators wished to discover what the descendants 
of the hybrids would be like. Only blue Andalusian fowls, hybrids, 
were chosen for this part of the experiment. This hybrid gener- 
ation is known as the Fi generation or the first filial generation. It 
was found that the offspring of hybrids varied in color. Some were 
blue like their parents, some were white like one grandparent and 
some were black like the other grandparent. When a large number 
of them were examined, it was found that the different colors of 
the chicks always occurred in the same proportion. For every two 
chickens that were blue like their parents, there was one black 
and one white chicken. In other words, 25 per cent were black, 
25 per cent were white, and 50 per cent were blue. This genera- 
tion, in which there was a reversal to ancestral type by the segre- 
gation of the original unit characters, is known as the second filial 
or the F 2 generation. Evidently, the original characters must have 
retained their identity since some of the offspring showed one char- 
acter and others showed the opposite character. 

The next step in the experiment was to find what would happen 
when the different members of this mixed group became parents. 
A black fowl was mated with another black and all the offspring 
were black. In other words, the black chickens of the F 2 gener- 
ation not only looked black like their black grandparents, but were 
pure as shown by the fact that they had only black descendants. 
They possessed only genes or character-determiners for black. 

A white of the F 2 generation was mated with another white and 



all their offspring were pure white. But when blue fowls were 
mated with others like themselves, some of their offspring were 


ft >W* *>$# *>£ 

If a black Andalusian cock is mated with a white Andalusian hen, the offspring is a hybrid 
showing a mottled blending of the black and white called blue. This is an example of incom- 
plete dominance. If a blue cock is mated with a blue hen, 25 per cent of the offspring will 
probably be black, 50 per cent may be blue, and 25 per cent may be white. Black pairs will breed 
only black; the white pairs will breed only white ; but the offspring of a blue pair will segre- 
gate, sort out, into black, blue, and white. 

black, some were white, and some blue. The blue chickens, then, 
of the F 2 generation were hybrids. 

The inheritance of color in the Andalusian fowl is : 

(1) Pure black mated with pure black will always produce pure 

(2) Pure white mated with pure white will always produce pure 

(3) Pure black mated with pure white will always produce 100 
per cent blue hybrids. 

(4) Blue hybrids, when mated with blue hybrids, tend to pro- 
duce 25 per cent black, 25 per cent white, and 50 per cent blue. 

The four-o'clock is another example of an organism in which a 
hybrid, produced by two distinct species, is unlike either, but is a 
blend of the two. The pure lines or types of four-o'clocks have 



either red flowers or white flowers. If red flowers are pollinated 
with pollen from red flowers, their seeds will produce red flowers. 
If white flowers are pollinated with pollen from white flowers, their 
seeds will produce plants with white flowers. But if red flowers 
are pollinated with pollen from white flowers, or white flowers with 
pollen from red flowers, the seeds will produce plants bearing pink 
flowers. This pink is a blend of the white and red colors. A 
flower of this type and the seed that produces it is called a hybrid. 
If these hybrids are allowed to pollinate themselves, their seeds 


The hybrids of the Japanese four-o'clock show incomplete dominance. The pure generation 
is usually called the parental, P ; the hybrid generation is the Fi ; and the next generation 
showing segregation is the F 2 . The little circles represent gametes and are colored to show 
genes or the color determiners which each flower carries. 


will produce plants which will bear flowers of three colors. 
Of every 1000 blossoms, approximately 250 will be red, 250 will 
be white, and 500 will be pink. The colors will be in the proportion 
of 1 : 1 : 2. The various colors of the four-o'clocks of succeeding gen- 
erations will vary in the same way as those of the Andalusian fowl. 

Experiments in plant breeding. Long before the foregoing 
experiments were carried on, Gregor Johann Mendel (1822-1884), 
an Austrian priest and head of a monastery, was especially inter- 
ested in cultivating garden peas. He found that his pea plants 
differed from each other in very many characters. Tallness, col- 
oration of seeds petals, and pods, and the hairiness, roughness, 
or smoothness of skin on the seeds and stems were some of the 
differences that he observed. Then he asked, " How does a partic- 
ular quality carry over generation after generation ?-" He pro- 
ceeded to seek the answer to his problem by experimentation. 
He selected tall plants and kept them in a certain garden plot. 
Away from these he raised a plot of plants that were always short. 
He called each group a pure-type. The unit character of height 
was one particular trait in which he was interested. He crossed 
pairs of plants which differed in this single character. He repeated 
his experiments to investigate other out-standing characters. Tall 
plants were crossed with short; plants with yellow seed coats 
with those of green seed coats ; plants having smooth seeds with 
those having rough seeds; hairy stemmed plants with hairless 
stemmed ones. In each of these crosses he watched the behavior 
of the variations of a single character only. After many experi- 
ments, Mendel learned and made known some very important 

The Mendelian laws of inheritance. — The Law of Dominance. 
When two of the pea plants that differed from each other in one 
characteristic were crossed, all the offspring resembled one of the 
two parents in regard to that characteristic. If one parent were tall 
and the other short, all of the next generation would be tall. 


Gregor Johann Mendel planted peas in his garden in Briinn, Austria. He crossed plants 
showing different characters and produced a variety of hybrids. 

If one of the parents were of a wrinkled-seed variety and one of a 
smooth-seed variety, all of the next generation would have smooth 
seeds. If one of the parents had a yellow seed coat and the other 
had a green seed coat, all of their offspring had yellow seed coats. 
To get more accurate results, he pollinated artificially the flowers 
of two varieties and kept them protected from all insects. The 
seeds from these plants were gathered, planted, and the new 
plants were carefully watched. Mendel found that the characters 
did not blend, as was later noted in the Andalusian fowl. One 
character completely dominated the other character and concealed 
it. This is called complete dominance. It has been found to occur 
in many species of plants and animals, and is true for many dif- 
ferent characters. This is known as Mendel's Law of Dominance. 
Dominance, as used in studies of heredity, is a condition in which 
one of a pair of characters will appear in the offspring and hide or 
mask the other. The character that shows in the offspring is 







T 2 




called the dominant character. The second quality, the one that 
does not show, although it is actually present, is known as 

the recessive character. 
Whatever there is in the 
protoplasm that pro- 
duces the recessive qual- 
ity, it is not destroyed 
in the crossing, for, as 
shall be seen, the quality 
may reappear in later 
generations. In the ex- 
ample given, the domi- 
nant traits were tall 
plants, smooth seed, and 
yellow seed coats. The 
recessive traits were 
short plants, wrinkled 
seeds, and green seed 
coats. The individual 
resulting from a cross of opposite characters is called a hybrid. 
For example, when plants with yellow seed coats are crossed with 
those with green seed coats, the offspring appear yellow. Because 
one of the parents had green seed coats the protoplasm of the 
offspring must be different. These yellow offspring are hybrids 
since they conceal the character determined for green. In all 
external appearances, hybrids resemble pure dominants. 

Mendelian Law of Segregation. Although the tall descendants 
of a mixed parentage, that is, a tall and a short, may appear tall 
like one of the parents, its protoplasm or part of its protoplasm 
is really different. This must be true since it has been built up 
in part from the protoplasm of the short parent. In the same 
way, the plant with the yellow seed coat of mixed parentage may 
resemble, in seed coat color, one of the parents, but it is still a 

When pollen from a pea plant that produces smooth seeds 
is transferred to a plant that- produces wrinkled seeds the 
resulting plants will produce smooth seeds. In peas, 
smooth seed coat dominates a wrinkled seed coat. The 
resulting offspring are hybrid, for when they are self- 
pollinated their offspring show 75 per cent smooth seeds 
and 25 per cent wrinkled seeds ; of the 75 per cent smooth 
seeds, 25 per cent is pure bred smooth, and 50 per cent is 
hybrid smooth. This illustrates complete dominance, be- 
cause smooth seed coat completely dominates wrinkled 
seed coat and does not blend with it. 



descendant of the green seed coat stock, and its protoplasm is 
probably different. Mendel made further experiments with his 
peas to find out what happened in later generations. He made 
three kinds of crosses: (1) he cross-pollinated a hybrid with the 
dominant parental type ; (2) he crossed a hybrid with the recessive 
parental type ; and (3) he crossed a hybrid with a hybrid. 

Consider the third experiment first. When hybrids were self 
pollinated, their seeds always produced species of both ancestral 
types. For example, hybrid peas with yellow seed coats produced 
seeds with both yellow and green coats. The hybrids must have 
carried greenness even though it did not show. There was a split- 
ting up, so to speak, of the combined inheritance into its two 
components, yellowness and greenness in the seed, or into domi- 
nance and recessiveness. This sorting out of members of a pair of 
factors is called segregation. This has been found to occur not only 
in hybrids but also when pure-breeding varieties are crossed. When 
large numbers of offspring of hybrids are considered and tabulated, 
the segregation is always in the proportion of one recessive to three 
dominants, of which one is pure and two are hybrids. 

• • 

; x ; 




\„ _ _ „ „ mm ./ 

Black dominates red in cattle. Name the three generations shown in the diagram. Note 
also on the sides of the diagram the result of what the animal breeder calls a back cross; i.e., 
hybrid with black and hybrid with red. 



When hybrids are crossed with pure dominants, the offspring 
will still retain the dominant appearance, but the recessiveness is 
not destroyed, for it may be made to reappear in later generations. 
These offspring are found to be, approximately, one half pure domi- 
nant and one half hybrid, although they may all look dominant. 

When hybrids are crossed with pure recessives, segregation again 
takes place. One half are recessive and one half appear to be 
dominants, but are hybrids. When hybrids are crossed with 
hybrids, or with pure dominants, or with pure recessives, the 
original parental characters tend to sort out. This, Law of Segre- 
gation, is perhaps the most important discovery that Mendel made, 
although it grew out of his discovery of dominance. 

Problem. What combinations of chromosomes result from maturation 
and fertilization f 

I. Place two black beans (to indicate chromosomes carrying black color) 
in the circle representing the egg mother cell, and two white beans (indicating 

mature eg£« Sperms 


^mother cell 

sperm another cell 

the chromosomes carrying white color) in the sperm mother cell. Assume 
that the chromosomes have the character-determiners or genes for color only. 

A. Move the chromosomes from the primary sex cell to the gametes to 
show the change that takes place during maturation (reduction division). 

B. Move the beans in the circles representing the sperms, so as to indicate 



fertilization of the eggs. Show the combinations of chromosomes in the 

C. Draw in the representations of the chromosomes (beans) . Color the 
black and leave the white uncolored. How will you represent the hybrids ? 

II. Repeat, the above experiment, using the hybrid combination of chromo- 
somes in the primary sex cells. Keep in mind that primary sex cells can be 
hybrid in regard to a particular character, but germ cells must be pure, 

tncrtwre egg* 6p*rms 

•g^nwlher celt \c-^']^~ZL~~\'~^J^'J'^ t,rTn ™>tke£cell 
A. Record combinations resulting from fertilizations. 

III. Repeat the experiment, using in the male primary sex cell the hybrid 
combination, and in the female primary sex cell two recessive white chromo- 
somes. Record by means of diagrams, the various possible combinations 
resulting from fertilizations. 

IV. Repeat the experiment, using hybrid in one cell and dominant black in 
the other. 

V. What law of heredity did experiment I illustrate ? What law of heredity 
did experiments II, III, and IV illustrate? 

Mendelian Law of Unit Characters. Another important contri- 
bution that Mendel made was his emphasis upon the study of 
single characters. In speaking of organisms, the general type is 
referred to rather than the individual traits that make up that 
type. Fox terrier, for example, or crimson rambler, describes a 
complete picture without the need of hundreds of details in which 



that particular variety differs from others. It is known, however, 
that the individual organism is a combination of thousands of small 

sperm carries 









"" : i! "- y 




An experimenter, Punnett, devised a method 
of predicting how genes combine after crossing. 
He used boxes known as Punnett squares. 

Turn to diagram on page 321. The gametes 
of the parent flowers carry only red, R, or no 
color, r. Note in the above diagram, all the 
possible combinations of gametes and observe 
the identical result Rr — a hybrid. 







T<a& ] 






r r 



The gametes of hybrid, pink four-o'clocks, 
carry either the dominant R or the recessive r. 
When fertilization occurs, the law of chance 
determines whether a pure dominant, a hybrid 
or a pure recessive is formed. Notice how the 
combinations are described with the Punnett 

differences, some structural, 
and some physiological or the 
result of physiological activity. 
The problem of heredity has to 
do with studies in respect to 
each of these individual char- 

After Mendel had assured 
himself that there was domi- 
nance and, later, segregation 
for each of several pairs of 
characters, he took up the 
problem of organisms that dif- 
fered in two characters. For 
example, some tall plants were 
hairy and some were smooth ; 
some hairy plants had yellow 
seed coats and some had green 
seed coats ; some of the yellow 
seed coats were wrinkled and 
some were smooth. By experi- 
ments in crossing for several 
generations, Mendel found that 
dominance and segregation oc- 
curred for each character inde- 
pendently of the other charac- 
ters, and so he formulated the 
Law of Unit Characters. 

Simply stated, it means that 
a pair of characters behaves in- 
dependently of any other pair 



of characters. This makes it possible to secure various combina- 
tions of characters not associated in the original pure stocks. For 
example, tallness is dominant to shortness, and yellow seed ~coat 
is dominant to green seed coat in peas. If a tall, green seed plant 
is crossed with a short, yellow seed plant, the offspring will all be 
tall with yellow seeds. Dominants conceal recessives. The fact 
that each parent had a dominant and a recessive trait does not 
interfere with the laws of heredity which state that the dominant 
traits conceal the recessive traits and each pair of characters be- 
haves independently. New combinations of characters are thus 
set up in the offspring. Offspring do not resemble either parent 
in all characters. 

Mendel worked eight years on his garden peas and was able, in 
1859, to present his results. At that time everybody was excited 
about Darwin's work. Few, in fact, none, had time for Mendel. 

In this breeding experiment, pigmentation and quality of hair of guinea pigs are the factors 
involved. R represents rough hair, r smooth hair ; B denotes black color and b white color or 
absence of black. The circles show the genes carried by body cells and matured germ cells. 
An animal of the Fi generation carries two pairs of characters and is known as a dihybrid. When 
dihybrids are bred, the F 2 generation segregate in the ratio of 9, 3, 3, 1. 
WH. FITZ. AD. BIO. — 22 



His paper was received in silence and soon forgotten. In 1900, 
sixteen years after his death and thirty-five years after his dis- 



























The Punnett square may be used to show the possible sorting out during maturation of germ 
cells of dihybrids and the various combinations resulting after fertilization. Each square repre- 
sents an individual. This square shows the possible combinations of genes in the nature of 
guinea pigs of different colors and types. The dominant characters are, large B, representing a 
pigmented coat, and R, rough hair. The recessive characters are, b, denoting white coat, and 
r, smooth hair. 

coveries, three other scientists working independently arrived at 
the same conclusion. Mendel's work was then given full credit. 

Since 1900, it has been proven again and again that heredity is 
frequently shown in animals exactly as in Mendel's peas. If pure 
black guinea pigs are crossed with pure white guinea pigs, all the 
resulting hybrids will be black, showing black to be dominant. 

The guinea pig and garden peas show complete dominance. 
The Andalusian fowls and four-o'clocks, in which the characters 
blend, show incomplete dominance. 

Summary. 1. A pure character is one that gives rise only to a 
character like itself. The plant or animal possessing it carries pairs 
of like factors ; for example, two factors for height, one paternal and 
one maternal. 

2. A plant or animal is a hybrid when it carries a pair of contrasting 
factors. For example, hybrid tall carries both tallness and shortness. 


3. Mendelian Laws of Heredity. 

a. Law of Dominance. When an individual, which is pure as to 
a particular factor, is crossed with another individual which is pure 
in the contrasting factor, only one of these factors will appear in 
the offspring. The character which appears is called dominant; 
the other which is inherited, but is concealed, is called recessive. 

b. Law of Segregation. 

(1) When hybrids are mated, the contrasting factors are seg- 
regated out in the proportion of 25 per cent pure dominant, 50 
per cent hybrid, and 25 per cent pure recessive. 

(2) When hybrids are mated with pure dominants, there is a 
segregation of 50 per cent hybrid and 50 per cent pure dominant. 

(3) When hybrids are mated with recessives, there results a 
segregation in the proportion of 50 per cent hybrids, 50 per cent 
recessives. , 

c. Law of Unit Characters. Every organism contains many pairs 
of factors. Each factor, as tallness or shortness, is inherited as a 
unit, that is, independently of the other and of any other pair of 

These laws were formulated by the study of the external appear- 
ance of the results of different matings. What caused it all? A 
difference in the protoplasms of the germ cells has been mentioned. 
This is true. Recent investigators have formulated a theory that 
has stood the test of much careful checking. The chromosome is 
concerned with heredity. It is thought that a certain part of the 
chromosome called the gene or character-determiner actually 
directs and controls the development of the individual char- 

Chromosome theory of inheritance. If both parents" are pure 
as regards a particular character, both the egg and sperm will 
contain the determiner for that character and the offspring will 
receive a double contribution of the determiner or " gene." For 
example, the genes of a pure tall pea plant will carry only tallness ; 
the genes in a pure dwarf pea plant will carry only dwarf ness. 
The offspring of such pure breds, whether dominant or recessive, 
cannot help but be pure. The offspring of the tall plants will be 


tall and those of the short will be short. Diagrams similar to 
Punnett's (on page 328) may be worked out. Use a capital 
" T " for tallness and small " t " (small letter indicates the lack of 
dominant character) for dwarfness. The gametes at the top of the 
squares are the sperms and those at the side are the eggs. The 
combinations in the squares will show the meeting of the chromo- 
somes in the fertilized eggs. 

Formulae. (1) T X T = TT. 

(2) t X t = tt. 

When the dominant character is present in one parent only, then 
the offspring will have only a single contribution of the gene. The 
offspring will appear dominant but will be a hybrid. 

Formula. TXt = Tt. 

What happens when hybrids are mated? It is believed that 
during maturation the contrasting factors of hybrids go into the 
separate eggs or sperms. Thus, the male primary sex cell will 
be hybrid, but one half of the sperm cells will carry the recessive 
factor and one half the dominant. Likewise, half the eggs will 
carry a dominant factor and half the recessive. In other words, 
the mature germ cells are always pure as regards any one 
character. The individual may be a hybrid but the gametes are 
never hybrid. 

When these gametes of hybrid parents join, the law of proba- 
bility shows that the following combinations are possible. 
T — >t 

Formula. X = TT > Tt > tT > u 

z ^ z 

When a hybrid is crossed with a dominant, the gametes of the 

hybrid will be half dominant and half recessive, while the gametes 

of the dominant parent will all carry the dominant gene. The 

following combinations are possible. 

T — >T 
Formula. X — TT. TT. tT, tT 



When a hybrid is crossed with a recessive, the gametes of the 

hybrid will be half dominant and half recessive, while the gametes 

of the recessive will all carry the recessive gene. 

T — >t 
Formula. X =T *> Tt > u > u 

Results are half recessive and half hybrid. 

Kind of Organism Dominant Character Recessive Character 

Wheat Late ripening Early ripening 

Wheat Susceptibility to rust Bearded 

Barley Beardless Immunity to rust 

Maize Round, starchy 

kernel Wrinkled, sugary kernel 

Cotton Colored lint White lint 

Sweet pea Colored flower White flower 

Cattle Hornlessness Horns 

Rabbits Short fur Angora fur 

Mice Pigmented coat White coat 

Leghorn chickens . . White plumage Pigmented plumage 

Canary Crested head Plain head 

Land snail Plain shell Banded shell 

Horses Black Chestnut 

Bay Black or chestnut 

Gray To all colors 

Man Curly hair ' Straight hair 

Dark hair Light ; red 

Brown eyes Blue eyes 

Normal pigmentation Albinism 
Broad fingers (lack- 
ing one joint) .... Normal length 

Questions and Suggestions 

1. Contrast somatic variations with germinal characters. 

2. Diagram, using the Punnett square, the. Andalusian fowls through 
two generations. 

3. Diagram, using the Punnett square, the Japanese four-o'clocks 
through two generations. 


4. State and illustrate the three Mendelian Laws. 

5. Using a pair of characters in wheat, show how it may breed 
through two generations, showing all possible combinations in the 
offspring. At the beginning of your Work, be sure to explain the rep- 
resentations you use for characters. 

6. Using a pair of characters in cattle, show how it may breed 
through two generations, showing all possible combinations in the off- 

7. Give a library report on the life and work of Gregor Mendel. 

Supplementary Reading 

Conklin, Edwin Grant, Heredity and Environment in the Development of Men. 

(Princeton University Press). 
Guyer, Michael F., Being Well Born; an Introduction to Heredity and Eugenics. 

(Bobbs-Merrill Co.). 
Journal of Heredity, American Genetic Association. Washington, D. C. 
Morgan, Thos. Hunt, The Physical Basis of Heredity. (J. B. Lippincott Co.). 
Shull, A. F., Heredity. (McGraw Hill and Co.). 
Sinnott, E. W., and Dunn, L. C, Principles of Genetics. (McGraw Hill 

Book Co.). 
Walter, H. E., Genetics. (The Macmillan Co.). 



Hugo de Vries. 

Keystone View Co. 
August Weismann. 

What are mutations f What is the importance of mutations f 

The theory of germ plasm. August Weismann (1834-1914), a 
German biologist, tried to produce a race of tailless mice. He 
cut off the tails of tiny baby mice as soon as they were born. When 
these grew to adult mice, they mated and had offspring. These 
baby mice had long tails. He repeated this experiment generation 
after generation. Cutting the tails of the parent mice did not 
affect the germ cells of either males or females. He then selected 
mice with the shortest of stubby tails, mated them, and continued 
to select the shortest-tailed mice for parents. After several genera- 
tions of this selecting and mating, a short-tailed race of mice was 
produced. He had selected mice whose germ cells carried the gene 
for short tails. 

As a result of this second experiment, Weismann formulated a 
theory explaining why offspring resemble their parents. He 
believed that the germ plasm does not arise anew in each organism, 
but is actually received from its parents. Explained briefly, his 
theory is this : Each new organism begins as a single cell, which is 
pure germ plasm. In higher plants, and animals this cell is formed 
from the union of an egg and sperm. The cell, called a fertile egg, 
begins to divide. Very early in this division, and before differ- 



entiation begins, one cell or more will be set aside to produce future 
germ cells. . The other cells go on multiplying and form the soma, 

er" son* grat^son grecnctson 

a piocsm-^, 

According to August Weismann germ plasm is derived from the germ plasm of previous 
generations. Thus it is continuous from one generation to another. Successive generations 
must resemble each other since they are all derived from the same germ plasm. Somatoplasm 
develops from germ plasm. 

or body cells. From the formei; cells, there develop all the germ 
cells of the organism. Germ cells consist of germ plasm, body cells 
of somatoplasm. When some of the germ cells of one individual 
meet the germ cells of another individual, they will unite, and, 
while still in the form of germ plasm, a small portion of it will be set 
aside to form the germ cells of the embryo. Thus the germ plasm 
is continuous from one generation to the next. 

This continuity of germ plasm has actually been demonstrated. 
One observer records that when, in a certain worm, the sixteenth 
cell stage of the embryo is reached, one cell is set aside to form the 
germ plasm and the other fifteen of the cells form somatoplasm. 

Mutations. It has already been stated that variations of the 
body plasm, which occur during the life of the individual, such as 
dwarfing of trees by wind and the acquiring of muscular skill, are 
generally considered not inheritable. These are often called 
acquired characters. Acquired characters are somatic variations 
which are due to environment and are not as a rule transmitted 
from parent to offspring. Some experimentation has recently been 
undertaken to show that, under certain conditions, acquired char- 
acters may be transmitted from parent to offspring. But, since 
these abilities were acquired by the soma cells long after the germ 



cell became separated from the body cells, investigators are 
having difficulty in explaining how the germ cells can transmit 
the acquired characters. 

However, a plant or animal will often appear, which, from the 
first, is so unlike its parents that it is called a freak or sport. For 
example, albino animals which have no pigmentation in fur, skin, or 
eyes are not infrequent. White rats have been developed as a 
distinct species from a sport which appeared as an offspring of 
rats with pigmented coats. Albinism is inherited as a recessive 
trait and is sometimes found in humans as well as other animals. 
This sudden departure from the ancestral type is called a mutation 
and the individual itself is a mutant provided the new species 

1st feneration 

2nSl generation 

33l generation 

4tk generation. 















rubri "nervis 













Hugo de Vries bred evening primroses through numerous generations. As his experiment 
progressed, he observed among them peculiar dwarfed individuals which bred true. He called 
these nanella. Then he isolated a type with unusually broad leaves which he called lata, and a 
type with reddish veins, the rubrinervis. In successive generations, he observed other plants 
with different characteristics. He preserved the new qualities by careful breeding. These 
were mutant primroses. 



Cattle originally had long horns. There appeared a mutant without horns. This animal 
became the ancestor of a hornless race of cattle. 

breeds true to its type. In Paraguay in 1770, there was born a 
hornless calf in a herd of ordinary long-horned cattle. Animals 
without horns are less dangerous to the other animals of the herd 
and also to their owners. Therefore, this animal was later bred 
with the ordinary cattle and it was found that the hornlessness 
was inherited as a dominant factor. Before this, cattle had some- 
times been de-horned, polled artificially, but from this one animal 
an entire race of hornless or naturally polled cattle was developed. 
The original hornless calf was a mutant. 

Short-legged sheep, which cannot jump walls, have been devel- 
oped from the long-legged Ancon sheep. Six fingers instead of 
five, two joints in the fingers instead of three, and webbed 
fingers are a few of the inherited modifications, mutations, that 
have been found in human beings. The navel orange (seedless 
orange) originated as a mutant in Brazil. 

The first person to use the term mutation was Professor Hugo 
de Vries of Holland. He was born in 1848 and was, for a long time, 
a professor at the University of Amsterdam, Holland. He carefully 
watched the descendants of one primrose plant for several genera- 
tions and found that it gave rise to seven distinct new species, each 
of which bred true. Each mutant differed decidedly from the 
others in height, shape of leaves, or some other character. 

Mutations are inheritable and there is little doubt that they are 



due to some germinal variation. They may be dominant or 
recessive in character. They are of tremendous economic impor- 
tance to man since valuable and desirable mutants can be used lis a 
starting point for a new species of plants or animals. De Vries was 
the first man to advance the theory that many of our present-day 
plants and animals possibly originated as mutants. 

Causes of germinal variations. Our ignorance concerning the 
causes of germinal variations is profound. We do know that slight 
variations are exceedingly common; no two living things, even of the 
same species, are exactly alike. Decided variations such as muta- 
tions are more rare, but when we become more observant we find 
them to be more frequent than, at first, believed. The following 
are some of the more common explanations of causes of mutations. 

(a) Changes in chromosome number. Scientists found that the 
original primrose had 14 chromosomes, but that the 7 mutants 
had respectively 15, 16, 20, 22, 24, 27, and 28 chromosomes. 
Other observers have also found at times a different number of 
chromosomes in other mutants. How or why the number of chro- 
mosomes changes is not yet definitely known. 


C B 

Chromosomes A and B sometimes bend around each other. Before they separate, part of 
B becomes joined to A as in C and part of A becomes joined to B as in D. This is called 
crossing over. Some of the factors originally in one chromosome are now in the other. 

(b) Change in the character of the gene itself. Morgan has found 
that most of the fruit fly (Drosophila) mutants that he has studied 



had the same number of chromosomes as their parents. There- 
fore, it may be assumed that when the chromosome number does 


^ r ing 




wing * 


r-<s2i eye 



T. H. Morgan and his associates have observed the appearance of hundreds of new characters, 
mutations, in fruit flies. 

change, a mutant is produced, but that germinal variations may 
also arise in other ways. Morgan has shown that mutations 
sometimes arise as a result of one gene or more actually changing 
in character. He has identified over 400 characters which are 
carried by the eight chromosomes of the fruit fly (four chromosomes 
in each germ cell). He believes that each character is determined 
by a gene in a chromosome. Therefore, there are many genes in 
each chromosome. Experimental work in heredity makes it seem 
highly probable that these tiny units of inheritance are present in 
the chromosome, and if they change in character it again seems 
plausible that a germinal variation would result. 

(c) Crossing-over of genes. Several scientists have done experi- 
mental work that would seem to show that sometimes the genes 
actually cross over from one chromosome to another. Just be- 
fore reduction-division, the chromosomes always arrange them- 
selves side by side in pairs. In the fruit fly there would be four 



pairs. Under the microscope it has been seen that the paired 
chromosomes have occasionally exchanged places. This is not a 
certainty, because, under the microscope, both members of a pair 
of chromosomes look exactly alike. But it can be seen that they 
become twisted. The experimental work makes the possibility 
seem highly plausible that some of the genes from one chromo- 
some of the fruit fly have crossed over to the other. 

(d) Decided changes in environment Doctor Tower of the Uni- 
versity of Chicago collected 40,000 potato beetles, grouped them 
into colonies, put them in glass cages, and subjected them to* varying 
degrees of heat and moisture. He found that the change in environ- 
ment had no effect upon that generation, but the eggs laid by these 
beetles produced offspring of a different color, which continued to 


temperature temperature 
lov humidity high humility 
ydtifaay v v tortuo$< 

parent/ jnelanothora^c rubicunaa 

Certain scientists are trying to prove that environmental conditions can produce changed 
characters in organisms, which will be transmitted to their offspring. Tower subjected parent 
potato beetles to certain varied conditions of temperature and humidity. The offspring showed 
new characters which they in turn transmitted. Some of Tower's mutants are shown in the 
above diagram. 

breed true as long as he kept the heat and moisture the same. 
Tower has been able to produce mutants by environmental 


changes. Other insects, such as butterflies and grasshoppers, have 
been known to produce mutants by a decided change in tempera- 
ture, food, and recently by the use of the X-ray. The treatment 
of parent fruit flies and mice with X-ray and radium rays has 
caused them to produce offspring with somewhat malformed 
bodies. These peculiar characters were handed down to the next 
generations. The germ plasm had been affected. It would seem 
that in some way the germ plasm is affected by the change in 
the conditions of the environment, causing mutations to appear 
in the second generation. It is not conclusively known whether 
a decided change in environment has ever produced mutants in 
nature as it has been done under experimental conditions in the 

Questions and Suggestions 

1. State the doctrine of continuity of germ plasm. How old is 
germ plasm? 

2. ' What are mutations ? Give examples. 

3. What is the relation of mutations to heredity ? 

4. What part did Hugo de Vries play in developing the theory of 
germ plasm ? 

5. Give three theories concerning the causes of mutations. 

6. Discuss Professor Morgan's work with fruit flies. 

7. Discuss Doctor Tower's work with potato beetles. 

8. Give a library report on the biography of August Weismann. 

9. Look up in a recent science book or magazine and report on the 
experiments that are now being carried on concerning mutations. 





Speed Horse. 

Dray Horse. 

What are some of the results of plant and animal breeding f What 
are some of the methods used by plant and animal breeders to improve 
the variety? 

Importance of plant and animal breeding. It is only a little 
over one hundred years ago that the English clergyman, Malthus, 
wrote his famous essay setting forth the principle that population 
tends to increase much faster than the supply of food. He believed 
that famines, wars, and plagues were useful, at least, in limiting 
the population that otherwise would be doomed to slow starvation. 

What is the situation to-day ? Since the time of Malthus, the 
population of Europe has nearly trebled, and in the United States 
it has increased approximately ten times. Yet famines are no 
longer experienced except in those countries with poor transporta- 
tion facilities. The world as a whole has at no time been so well- 
fed nor had so great a variety of foods. Malthus contributed a 
fact of real value to mankind in calling attention to the rate of in- 
crease of the population. Since that time, modern farm machinery, 
good transportation, and knowledge of food preservation have all 
aided an increasingly smaller proportion of the people of the world 
to provide sufficient food from the farms for the needs of all. 

Another factor which has greatly increased the production of 
food, and which is of particular interest to the biologist, is the 



improvement of food-producing plants and animals. The cattle 
of the Middle Ages were about the size of the average calf of to-day, 
but through many generations of selective breeding the size of 
cattle and their yield of milk have been increased to a remarkable 

Alfalfa is especially hardy. It withstands droughts, and it may 
yield as many as nine cuttings a season. Due to careful selection 
of seeds and cultivation of the ground a field of alfalfa will furnish 
sufficient food for three to six times the number of cattle which 
it formerly supported. Plant breeders have Keen able to increase 
the amount of sugar in beets so that the number of pounds of beets 
needed to make one pound of sugar has decreased from eighteen 
pounds in 1836 to seven pounds in 1904. Luther Burbank im- 
proved the potato by making it resistant to a disease called the 
potato blight, and by increasing its starch content. It is said, 
that this species of potato adds seventeen and one half million 
dollars to the farm incomes each year. 

One of the best dairy cows of recent years, gave 20,616 pounds 
of milk and 1005.9 pounds of butter fat in one year. She gave 
more than her weight in milk each month. Contrast this cow with 
a prize cow of 1904, that gave 567 pounds of butter fat in one 

Every day our agricultural experiment experts and other scien- 
tists are improving our foods. These products are not produced 
in a haphazard way. They are frequently the results of careful 
experimental breeding. It is, however, only within the last 
twenty-five years that sufficient knowledge of the laws of heredity 
has been available to put plant and animal breeding on a scientific 

It is the plant breeders concern to increase the food content of 
grains and fruits, to produce new species immune to disease, to make 
certain varieties hardy so that they can be grown in more northern 
climates, and to hasten maturity. The average yield per acre 



of wheat was between 10 and 15 bushels per acre. By selection and 
cultivation, the yield per acre has been increased to over 40 
bushels. - Wheat has been bred so that several species now combine 
the desirable qualities of large yield per acre, good quality for 
bread making, hardiness, resistance to rust, and resistance to 
drought. The ordinary corn stalk usually produces but two or 
three ears. But through experimentation, corn has been produced 
with stalks 16 feet high and which bears 32 ears to the stalk. 

The particular aims of plant and animal breeding are to 
establish varieties immune to disease, to produce new species, to 
breed for desirable characters, to improve quality by proper selec- 
tion and to make both old and new forms more productive. 

Immunity to disease. In some of the Southern States, the 
cattle had long been subject to Texas fever which was easily 
spread and caused the loss of 
many cattle. It was learned 
that the wild Brahmin cattle of 
India were immune to the dis- 
ease. Their jlesh, however, 
was not valuable as beef. Two 
strains, our southern cattle 
and the wild Brahmin, were 
crossed. Immunity to Texas 
fever was found to be domi- 
nant in the Fi generation. 
These hybrids were mated 
again and from the F 2 genera- 
tion only the immune animals 
that seemed to show the best 
beef tendencies were selected 
and bred. By careful selection 
a species of cattle combining both immunity and good beef 
qualities was thus obtained. 

WH. FITZ. AD. BIO. — 23 

U. S. Devi. of Agric. 
Animal breeders have produced from the orig- 
inal wild strain of pig shown above the fine 
specimen shown below. Compare the food value 
of the two specimens. 

An average dairy cow gives approximately 8304 lbs. of milk per year containing from 130 to 
300 lbs. of butter fat. The daughters of a famous sire, Fauvic's Prince, averaged 17,135 lbs. 
of milk per year. Their average yield of butter fat is 801 lbs. per year. Fauvic Star, the middle 
cow on the right broke all records with 30,616 lbs. of milk and 1005.9 lbs. of butter fat. 



* 347 

A certain fungus disease in wheat is recessive. In 1906, from 
a field of badly infected wheat in Kansas, a lone plant was dis- 
covered that showed no signs of rust. This single stalk was 
probably a mutant. It was tested, propagated, and the offspring 
were carefully selected for immunity as well as for the desirable 
qualities of the parent 
wheat. An immune spe- 
cies that also gave an' in- 
creased average yield of 
four and one half bushels 
per acre was finally pro- 
duced. In 1917, this strain 
of wheat, called Kanred (a 
combination of Kansas and 
its color — red), was dis- 
tributed for commercial 
use and has already in- 
creased the wheat income 
in Kansas by many million 
dollars per year. The 
same procedure was fol- 
lowed in combating a 
blight that often affected 

An immense amount of 
damage is annually done 
by corn smut. Some 
sound ears were found in fields of corn that were badly infested 
with corn smut. The sound ears were selected and bred until an 
immune variety was obtained. 

Production of new species. A white blackberry sounds like 
a paradox, but we use the term in referring to a new blackberry 
developed by Luther Burbank. He noticed a wild fruit, bitter, 

Underwood & Underwood 
Corn has been improved through careful breeding. 
Desirable characters such as number of kernels, food 
content of kernels, regularity of formation of kernels 
and size of ear have been combined in the same corn 
plant. A prize red corn of Kansas is shown in the 


small, and really a light yellow rather than white. It was, without 
a doubt, a member of the blackberry family. He hybridized this 
by crossing it with the Lawton blackberry which was black, large, 
juicy, and of pleasing flavor. He found that black was dominant 
over the light yellow. In the F2 generation the light color again 
appeared, and by selecting for several generations only the plants 
for breeding that combined the lack of color with the desirable 
flavor and size, he obtained a large tasty berry that is now known 
as a white blackberry. 

Some varieties of plants have been improved in many different 
ways. Luther Burbank studied various kinds of plums obtainable 
here and in other countries. He crossed American, Japanese, and 
European kinds. Then he selected the best for further experi- 
mentation. As a result, he obtained different species : (1) of 
many varieties in the coloring of skin and the texture of flesh; 
(2) of a wide variety of shapes; (3) of a wide variety of new 
flavors and aromas ; (4) of sizes that are increased to three inches 
in length and two and one half in diameter; (5) that produced 
either early or late species. (Some ripen a month before the 
earliest of the old varieties; others ripen as late as December.) 
(6) that are not affected by the frost or cold weather. Some 
plums have been developed that can be shipped long distances 
without spoiling. A species has been produced that can remain 
on the tree a month or two in hot weather without decaying, 
unlike the old varieties which had to be picked as soon as they 
were ripe. Some trees bearing these new varieties will begin 
to bear abundantly the third year if cuttings from young trees are 
grafted upon trees of ordinary size. 

Some of these new plums grow in climates and under conditions 
where the plum has hitherto been a failure. The Beach plum is a 
wild species growing along the coast. It is a low, spreading shrub 
with a small bitter fruit. It is very prolific and is resistant to cold 
and frost. This was crossed with an American plum. The result- 



ing species, called the Im- 
proved Beach plum, bears 
very abundantly. It is a de- 
licious plum, of very fine flavor 
and with a small stone. It is 
indifferent to frost, and bears 
under the most trying condi- 
tions of soil and climate. 

A cross between a plum and 
apricot has been produced by 
Luther Burbank. It is called 
the plumcot. He also pro- 
duced a stoneless plum. 

Breeding for points. Seed- 
lessness has sometimes devel- 
oped as a mutation. The 
seedless navel orange origi- 
nated as a mutant in Brazil. 
Twigs from it were grafted on 
to ordinary orange seedlings. 
Two of these tiny plants 
thrived, and from them, prop- 
agated by grafting, all of the 
navel oranges have been pro- 
duced. The value of vegeta- 
tive' reproduction as a means 
of making a new species breed 
true to type is very great. 
Since this makes use of the 
body plasm, it will continue 
to produce other plants like 
itself. For instance, if a breeder has produced a large, double- 
petaled, red-flowered dahlia, he may be sure that the bulbs of this 

The Lawton blackberry. 

The white blackberry that was crossed with 
the Lawton blackberry. 


dahlia will give rise to large double blossoms colored red. If he 
plants the seeds, however, he will probably find outcroppings of 
the plant's ancestry in the way of small flowers, some single rather 
than double, some with white petals, and so on. The potato at 
present rarely bears seeds. When such seeds appear and are 
planted, different kinds of potato plants may result. Many of 
these plants may bear potatoes that are small, irregular in shape, 
and low in food content. They closely resemble their wild an- 
cestors. Therefore, the potato is propagated vegetatively by 
using parts of the tuber containing the " eyes." Tomatoes were 
formerly small, tasteless, and full of seeds. But through selec- 
tion and cultivation, many splendid varieties have been developed, 
within the last generation. Other details that have been brought 
out through breeding are : increased egg laying in hens, increased 
milk supply from cows, and increased starch and protein produc- 
tion in corn. 

Improved quality. The southeastern region of the state of 
Washington was an excellent locality for growing wheat. But 
the climate is so severe that every three or four years, the entire 
crop was killed by frost. The problem of producing a hardy 
variety of wheat was turned over to Mr. Spillman of the United 
States Department of Agriculture. He selected as a beginning, 
the Little Club wheat, named for the short, clublike appearance 
of the head. It was desirable because it had a stem strong enough 
to resist storms and a head that remained closed long after ripen- 
ing. Thus the ripe grain was protected and was not likely to be 
lost before harvesting. This species was crossed with other varie- 
ties, including a hardy winter variety that would resist frosts. 
After ten years of careful selection and propagation, an improved 
frost-resistant variety of Club Wheat was obtained, that is now 
grown in the extreme Northwest. Winter character was found 
to be dominant over spring character and the club head to domi- 
nate over long head. 



This white leghorn hen established a record by 
laying 321 eggs in 51 weeks. 

Increased production. In 
almost all plants and food 
animals, a great increase in 
production has been brought 
about and there is still room 
for much improvement. 
Careful selection of the best 
types for breeding is a very im- 
portant factor here. Burbank 
increased the food content of 
the potato by 25 per cent ; 
Kanred wheat, merely through 
vigilant selection of the most 
productive plants for seed, sur- 
passed its parent wheat by an 
increased yield per acre. The 
average cow's milk will pro- 
duce 125 pounds of butter per 
year, but a Jersey cow will 
usually produce over 1000 
pounds of butter in a year. 
A 300-acre field in southern 
Illinois was planted with im- 
proved corn and yielded 30 
bushels more per acre than 
the fields planted with the 
ordinary seed. 

Methods of breeding. 
Hybridization is the crossing of 
two individuals carrying unlike 
characters. This has the ad- 
vantage of combining the desirable characters found in the two 
individuals into one individual. 

This barred Plymouth Rock hen laid 287 eggs 
in a year. The American egg record for three 
consecutive years was 282 eggs and 281 eggs 
made by two Barred Plymouth Rocks, and 303 
eggs from a hen which was a cross between a 
white leghorn and a Barred Plymouth Rock. 


Artificial selection. Many experiments in breeding start with 
hybridization, but they would be of little value unless the indi- 
viduals showing undesirable traits were disregarded and only those 
showing the desirable characters kept for breeding. This is called 
artificial selection. Even so, the organisms showing the useful 
traits will oftentimes not breed true as they are hybrids. To be 
successful and establish the desirable qualities, large numbers of 
matings must be tried out and only those that breed true should be 
retained. As has been said before, when vegetative propagation 
is possible, it is a certain means of breeding the plant true to type. 
Improved kinds of fruit trees are propagated only by grafting. 

Method of plant propagation. The typical method of plant 
propagation was that used by Burbank. The flowers which are to 
furnish the pollen are carefully gathered a day or so beforehand. 
The pollen is sifted from the flowers and kept in a cool place. The 
tree to which the pollen is to be applied is deprived of most of its 
blossoms in order that the remainder may be sure to develop and 
that there may not be too many to be properly looked after. The 
buds of the remaining blossoms are prepared for artificial pollina- 
tion by cutting away the petals and the .attached stamens. The 
pistils and stigmas are left uninjured and are protected from in- 
sects. Since there are no brightly colored petals to attract them, or 
anything for them to hold on to when entering, bees seldom ap- 
proach these flowers. If there is any danger of insects visiting 

the flowers, a paper bag is fre- 
quently tied over each individ- 
ual flower. When the pistil 
ripens, the pollen is applied by 
dipping a brush or finger into 
this yellow powder and touch- 

aae^h American ^^ ing the stigmas. All of the 

pixxm. plw«w best seedg that develop from 

The size, flavor, and quality of plums have been . . . . .. , 

improved through selection and cultivation. tne truit 01 the pistil tUUS 



treated, are saved and planted. When these new plants produce 
fruit, only the best seeds are selected. Frequently, the young 
plants are grafted upon other 
trees to hasten the growth. Hy- 
bridization is but the beginning 
of breeding. Careful selection 
must be continued, so that a pure 
type is established. 

Methods of animal propaga- 
tion. If a mutant with a desir- 
able character is found, it is bred. 
In case the new character is dom- 
inant, it will appear in the Fi 
generation, but the animal of this 
generation will be hybrid. This 
hybrid is then mated with an 
animal which shows the same 
desired character. Sufficient 
matings must be made to get 
the character in a pure form. 
This sometimes necessitates close 
breeding. By close breeding is 
meant mating individuals closely 
related, as grandparent with off- 
spring of the second, third, or 
succeeding generations. The fact 
that animals frequently take a number of years to mature is 
a serious difficulty met with in animal breeding. Close breed- 
ing does not necessarily reduce the vigor, but, if there are unde- 
sirable characters present, they may be doubled and the offspring, 
then, cannot be used for breeding purposes. In case the new 
character is recessive it will not appear until the F 2 generation. 
Then, if two individuals of different sex of this generation pos- 

The Beach plum grows in clusters. It is a 
small plum, smaller than the American plum. 
When these two plums are crossed, an im- 
proved plum, much larger than either parent, 
is produced growing in bunches, like the 
parent Beach plum. 


sess the desired characters, and are mated, their offspring will 
usually be a pure type. 

Questions and Suggestions 

1. What bearing has plant and animal breeding on the food situa- 
tion of the world ? 

2. Why is scientific plant and animal breeding a comparatively 
recent development? 

3. State five aims of plant and animal breeders. 

4. Describe in detail an example of each aim mentioned in 
question 3. 

5. Describe in detail how a particular trait may be established. 

6. What two biological principles are involved in breeding experi- 
ments ? 

7. State three difficulties animal breeders encounter that are not 
encountered by plant breeders. 

8. Look up and report on the life and work of Luther Burbank. 

Supplementary Readings 

Osterhout, W. S. V., Experiments with Plants (The Macmillan Co.). 
Sinnott & Dunn, Principles of Genetics (McGraw-Hill Book Co.). 



Sir Francis Galton. 

Underwood & Underwood. 
Charles Davenport. 

What is the importance of eugenics f What is the difference between 
eugenics and euthenicsf How can eugenics and euthenics be applied 
practically f 

Eugenics is the division of biology that deals with the improve- 
ment of the human race. It is a new science built upon an applica- 
tion of what we know concerning the laws of heredity. It also 
includes the study of how to improve the environment, although 
the effect of environmental conditions on people is frequently 
referred to as euthenics. 

History of the eugenics movement. In 1883, Sir Francis Galton, 
an Englishman, became interested in the science concerned with 
the improvement of the human race, to which he gave the name 
eugenics. He had in mind the improvement of human character- 
istics through heredity. In 1921, the Second International Con- 
gress of Eugenics stated that eugenics was the self-direction of 
human evolution. This means that individuals through good or 
poor marriages, can improve or impair the mental or physical heri- 
tage of future generations. The science of heredity has contrib- 
uted much to eugenics. Many family histories have been inves- 
tigated and different physical and mental traits have been traced 
through generations, with the utmost care. These investiga- 




tions have given data for the practical applications of eugenics. An 
Eugenics Laboratory is located at Cold Spring Harbor, Long Island, 
under the supervision of Dr. Charles B. Davenport. Research in 
the science is being carried on there by the most careful specialists. 
Methods of investigation. — Families of superior ability. 
Human heredity has not been studied by the experimental method 
as successfully as animal and plant heredity have been stu.di|df 
There are three reasons for this failure : (1) The length of life Bso 
long that no investigator can live long enough to study, personally, 
the heredity of more than two, three, or possibly four generations 
of a family ; (2) the number of offspring is small and it is difficult to 
draw valid conclusions from the limited data offered ; and (3) our 

□ o 

male female 

^marriage line 


4r- ciescent line 

■T~j s. parents 



"Koman figures 
cct left inciicate 
gene r-at ion^ 

s l=<iViIaren- 


^B.ie3L in. 

Arabic figures 
locate ^ 
xnd.iv i cltf ccl jS 


m. q 



alcoholic blin2L d>af epileptic feSS^L insane normal jtubeaallar 

The Eugenics Record Office at Cold Spring Harbor has adopted a standard set of symbols 

used in chart making. 

social customs handicap the work in this research, as people con- 
sider family affairs private and will not give information freely. 


Sir Francis Galton applied the statistical method to the study 
of heredity in human beings. By this system, the pedigrees of 
many families have been traced for generations and studied lis a 
means of determining what traits seem to occur most frequently 
in a majority of the descendants. Such a study has been made of 
the family of Jonathan Edwards. He was born in 1703 and was 
noted for his strength of character and for his high mental ability. 
In 1900, 1394 of the descendants of Jonathan Edwards had been 
traced and the life work of many of them discovered. They 
included many college presidents, professors, lawyers, doctors, able 
business men, and state officials. The group as a whole was 
highly intelligent and capable, with a high sense of civic respon- 
sibility. Their historian states that it is not known that any of 
them were criminals. The Edward family indicates that high 
mental ability is inheritable. 

An investigator recently tested a number of children for intelli- 
gence. Forty-one showed superior intelligence. What of their 
immediate ancestors? Of the forty-one, the investigators found 
that only two lacked a near relative with a superior intelligence 
rating. Definite talent in some form was found in different 
members of the families of these children. A study has been pub- 
lished concerning the intelligence of some students of Oxford Uni- 
versity, , England. The records of boys who secured marks of 
" honor " and " pass " were compared with the records made by 
their fathers. Of the " pass " students only twenty per cent of 
the fathers had taken first or second honors. That means they, 
too, were only in the " pass " class in their school days. On the 
other hand, of the students taking first honors, nearly forty-two 
per cent of the fathers had taken first or second honors. 

Woods has made, a study of several royal families, in which a 
comparison is made between parents and offspring in mental and 
moral qualities. There is a very marked similarity and uniformity 
shown in the results of this study. A resemblance between 


grandparents and 'grandchildren is evident though not as notice- 
able as closer relationships. Outstanding groups of individuals 
have descended from Peter the Great of Russia, William the Silent 
of Holland, Isabella of Spain, and Gustavus Adolphus of Sweden. 
Th3se studies have shown that men of the type of the Sidneys, 
Balfours, Cecils, and Churchills in England, and the Lowells, 
Eliots, and Dwights in America are not the result of chance or 
accident, but that their superior abilities are inheritable traits. 
When an exceptional man chooses an exceptional wife, the ma- 
jority, if not all, of their children will probably be exceptional. All 
members of royal families are not superior. There are some groups 
that show insanity, imbecility, and other mental defects, because 
these traits have been introduced through marriages with mental 

There seems little doubt that a certain stock or family will pro- 
duce men of great ability more frequently than will another stock 
or family. It is almost certain that the quality of mind and body of 
the parents will affect the offspring. Parents, sound in mind and 
healthy in body, tend to produce normal healthy children. 

Families of inferior ability. Parents physically weak and of a 
low-grade mentality will give to the world undesirable progeny, 
probably physically unfit and with mediocre intelligence. An 
American family which has been given the fictitious name of 
" Juke " has been carefully traced through a large number of 
generations. This family record starts with a shiftless vagabond 
born in New York state in 1720. In 1915, students had traced 
2094 members of this family: 1600 were feeble-minded or epi- 
leptic, 310 were paupers, 140 were convicted criminals, and large 
numbers of the remaining group were traced through the records 
kept in workhouses and other public institutions. This family by 
1915, had already cost the state of New York more than $2,500,000 
and the expense still goes on. Their descendants will continue to 
bear the same traits. The mental ability of this family is very 



low. Only twenty have been known to learn a trade and ten of 
these did so while in state prisons. 

The story of the Juke family indicates that weakness of char- 
acter and low mental ability will give rise to offspring with little 
moral or mental stability. Although this study does not prove 
that a tendency toward wrong-doing is inheritable, it certainly 
does show, at least, that weak character and low mental ability 
give rise to a person who often becomes a .criminal. The Jukes 
lack the judgment, memory, and will power that enable people to 
fulfill responsibilities toward their fellow men. 

The Kallikak family (the name is fictitious) throws still more 
light on human heredity. Martin Kallikak, a normal, healthy 

feeble min&eSL mother 

Intelligence and lack of intelligence seem to be inherited characters. One of the lines of 
descent of Martin Kallikak shows feeble-mindedness inherited from a feeble-minded mother. 
Of 480 descendants studied, only 46 were known to be normal. The other line of 496 descend- 
ants from Martin Kallikak and a normal wife was practically all normal. 

young soldier who fought in the American Revolution, had a son 
by a feeble-minded girl. This son had a family of ten children from 


whom there are 480 known descendants. Of these, only 46 are 
known to have been normal while 143 were feeble-minded. Knowl- 
edge concerning the others is missing or doubtful. After the war, 
this same soldier, Martin Kallikak, married a normal woman. 
From this union there have been 496 descendants ; none of whom 
were feeble-minded. The history of the Kallikak family indicates 
that feeble-mindedness is inheritable. The defective descendants 
were incapable of earning a living and some could not provide for 
themselves nor care for their physical comfort. It is necessary 
that these defectives be fed and sheltered, but it is more impor- 
tant that they be segregated in institutions where they cannot 
produce more offspring like themselves. 

The number of mental defectives in England and Ireland has 
been estimated to be about five per cent of the population. In 
1923, in the United States there about 267,600 mental defectives. 
The annual cost of caring for these persons was nearly $80,000,000, 
to which should be added three hundred millions of dollars which 
was the corresponding loss in industrial activity of these depend- 
ent people. In some states, one eighth of the total state expen- 
ditures is for the care of the insane. 

The cost of crime in the United States is ten billion dollars an- 
nually. Over twenty per cent of the inmates of jails, almshouses, 
and other institutions are foreign-born, although only fourteen per 
cent of the total population is foreign-born. There seems to be 
twice the number of foreign-born as native-born among the defec- 
tive group which includes the feeble-minded, insane, epileptics, 
criminals, blind, deaf, paupers, and other dependents on a com- 
munity. This is probably due to the fact that many foreigners 
of poor stock were formerly admitted to this country, but such 
undesirable aliens are now excluded. Therefore, the above figures 
include the people admitted before our immigration laws were so 
strict. They also show the necessity of a careful physical and 
mental examination of all immigrants to this country. 


A study of the records of 447 criminals showed that among 
their parents, 10 per cent were criminals, 6 per cent were victims 



■ boat 

W artistic 

W\ musical 
P -mechanical 
fl litemr^ 
I 1 normal 

x So^o5i5ip5i|Oio 

The Herreshoff family is noted for special skill in boat designing and building. Many cup 
winners have come from their yards, some of which have competed with Sir Thomas Lipton, 
challenger. The above chart includes one line of descent of the family. The entire genealogy 
has been traced and is recorded in the Eugenics Record Office at Cold Spring Harbor. 

of hysteria, 4 per cent of epilepsy, 15 per cent of alcoholism, and 
9 per cent of insanity. In a study of the inmates of certain 
penal institutions, 20 to 30 per cent were found to be mentally 
subnormal. Some, however, were normal and some very keen. 
Yet crime and mental deficiency are usually closely related. A 
criminal type, as such, does not exist. When people of low in- 
telligence are trying to fill positions which put too great a demand 
on their mental ability, they frequently lose their positions. Not 
understanding the cause, and, in some cases, being unable to get 
work, they remain idle. This makes them desperate and fre- 
quently leads them into bad and vicious company. When low 
intelligence is combined with emotional instability, the unfortu- 
nate persons frequently become wayward and turn to crime. 

From these and similar investigations it has been ascertained 
that desirable traits in man, such as high intelligence, without 

WH. FITZ. AD. BIO. — 24 


which we cannot develop will power, self-control, or a high moral 
responsibility, are inherited. Other studies indicate that special 
aptitudes such as musical or artistic ability as well as mathema- 
tical and inventive aptitudes, literary ability, and retentive mem- 
ory are inherited. On the other hand, a startling number of 
feeble-minded people and those of low mentality are responsible 
for the large criminal and defective groups that fill our chari- 
table and public institutions. 

Race improvement. There are two ways of improving mankind. 
This improvement may be called " human conservation." One 
method of bettering the race consists in giving every child the best 
possible inheritance. This is eugenics. This requires thought- 
fulness in selecting a mate so that the children will have desirable 
traits. Another method is to improve the environment of every 
individual and to give him the best possible opportunity to develop 
his capacities. It is true that anything which safeguards the 
health of the present generation also helps to safeguard the next. 
This second method is euthenics. It might be called the science 
of learning to live well. It consists of an endeavor to improve 
the individual through improving his environment and his training. 
If all people understood and practiced eugenics — being well born 
— and euthenics — living well — the world would be greatly im- 

The Eugenics Laboratory has collected many valuable statistics 
and data on human heredity. Research work is continually going 
on. If a man and woman contemplate marriage and question 
the possibility of some undesirable trait in one or both of the 
families being transmitted, the Eugenics Laboratory will give 
an opinion on the desirability of the marriage. For instance, if 
there is a tendency to deafness in one of the families, with perhaps 
some members being deaf mutes, there would be a double possi- 
bility of the children inheriting deafness if the family of the other 
prospective parent had the same trait, even though in a milder 


form. In some states marriages of first cousins are prohibited 
by law. The biological reason for this is made clear by the ex- 
ample above. If an undesirable trait runs in a family, both 
parents would be likely to carry it and there would be a double 
possibility of their children inheriting it. 

Suggestions for race improvement. (1) Segregation of the 
feeble-minded and prevention of their marrying are obvious 
methods for eliminating defectives and increasing the mentality 
of society as a group. Most states support such people in insti- 
tutions. This is a very costly method. A method that shows 
great promise is the colony system used in some parts of New 
Jersey. The mental defectives are kept in colonies, the men sep- 
arate from the women. They are all taught trades, and may 
travel in groups through the state under the strict supervision of 
guards. They do some road building, farming, and simple tasks 
which are parts of other industries and require little intelligence. 
In this way they earn money and help to maintain themselves. 

(2) As far as possible, the insane, criminal, and diseased should 
also be prevented from marrying. If they could be kept in in- 
stitutions, and have no offspring, the number of defectives in the 
succeeding generations would be gradually diminished. 

(3) All people should have an understanding of the value of 
eugenics. This is made possible by teaching pupils in high schools 
and colleges, the part played by inheritance in the life of 
every one, and to what extent certain characteristics or tendencies 
may be inherited. An enlightened public consciousness must be 
developed all through the world, if racial progress is to be made. 

(4) Certain laws in relation to marriage might be enacted and 
enforced. Each person desiring to marry should be compelled by 
law to pass a physical examination to determine whether he is phys- 
ically fit, or whether he possesses certain defects that would make it 
unwise for him, from an eugenic point of view, to marry and prob- 
ably pass on these disabilities. Some states already have such 


laws in operation. Wisconsin has enforced such a law since 1914. 
In this state the people show an intelligent interest in their health. 
Before any man may receive a license to marry, he must have a 
thorough health examination. If an applicant for a marriage 
license is told that he has a disease which makes it unwise for 
the marriage to take place, in most cases such a person is interested 
in learning how to overcome the handicap so that he may marry 
at some future time. The enforcement of this law is having a 
beneficial effect on the health of the people, as a whole, and it cer- 
tainly will mean better health for the next generation. When 
such laws are in operation, only the fittest are selected for parent- 

(5) The environment may be improved by enacting and enforc- 
ing laws concerning : 

(a) The eight-hour day 

(b) Better tenement and housing conditions 

(c) Public playgrounds for city children 

(d) Compulsory education 

(e) Laborers' compensation laws 
.(f)- Widows' pensions 

(g) Child Labor laws ' 

(h) Vocational guidance and training 

The eight-hour day permits a man to live a normal life with 
sufficient opportunity for education, recreation, and physical re- 
laxation. Better tenement and housing conditions will give all 
children opportunities to grow up in a clean, wholesome environ- 
ment. All houses should be built so that fresh air, sunlight, and 
good sanitation will be available for every person, no matter how 
rich or poor he may be. Public playgrounds for children will 
prevent accidents that kill and maim so many children who have 
no place to play except the streets. 

The compulsory education laws vary in the United States. Most 



of them insist- that all boys and girls remain in school until they 
are at least fourteen years old or have the equivalent of six years 
of schooling. But, in some sections of the country, these laws^are 
not enforced at all, while in other sections boys and girls are re- 
quired to remain in school until they are seventeen years of age or 
have graduated from a secondary school. The schools are the 
medium through which the home and the community are edu- 
cated. They are a direct means of raising the standards of living 
all through the country. Schools are also the most efficient means 
of ridding people of unhygienic racial and social customs. 

Many state compensation laws guarantee that a man's family 
will be cared for in case he meets with an accident. Even though 
this compensation may be small, it is of some value in helping to 

Brown tiros. 
A typical group of immigrants at Ellis Island awaiting admission to the United States. 

maintain a good or at least a decent environment for the family of 
such a person. 

In various states, laws have been enacted which provide pensions 



for widows who are in need. Some of these laws even provide for 
orphans up to the age of fourteen or of eighteen years of age. The 
average grant usually varies from one hundred to two hundred 

dollars per year for each 
child. In many cases, 
the law demands that 
the mother be a fit per- 
son physically, mentally, 
and morally, if she is to 
receive the pension 
which enables her to keep 
her children with her. 

Previous to the intro- 
duction of the modern 
factory system in the 
eighteenth century, chil- 
dren were commonly em- 
ployed in factories. 
Authorities of pauper 
institutions in Great 
Britain permitted pauper 
children to work as much as sixteen hours a day. In 1847, the 
hours for child laborers were reduced to ten hours a day. To-day, 
in most states of the United States a boy or girl may leave school 
at the age of fourteen and obtain working papers. In many 
states this is conditioned on the passing of a health examination. 
Five states of the United States are said to furnish one third of 
the total child laborers and one half of all child illiterates in the 
country. Congress has twice tried to pass laws regulating child 
labor but each time the law has been declared unconstitutional. 
In order for children to develop physically and mentally to the 
fullest extent, it would be wise to keep them out of factories and in 
school with suitable childhood recreation until, at least, the age of 

Immigrants are examined at Ellis Island to make sure 
that they are physically and mentally fit. All those 
suffering from mental disorders or from contagious dis- 
eases or who are, otherwise, physically unfit to make re- 
sponsible citizens are excluded from the country. 


fourteen. In some European countries, children under eighteen 
are not permitted to work at night or at hazardous trades. In 
many of our states the minimal age for hazardous trades such as 
quarrying and mining is sixteen. There is agitation in many 
states to keep boys and girls in school until the age of seventeen. 
They will then stand a better chance to enter industry with a 
fairly good physical and mental equipment. 

Vocational guidance and training are invaluable in directing chil- 
dren into vocations for which their intelligence seem to fit them. 
When properly directed, people with superior intelligence should 
be able to get established earlier than they usually do. Less gifted 
children should be advised to do that type of work which they can 
do rather successfully. This will give them a feeling of satisfac- 
tion in their work, which will make for contentment and happiness 
When people are continually losing their jobs, due to their inability 
to perform the tasks given, idle and vicious habits usually result. 
Continuation and trade schools are invaluable aids in teaching chil- 
dren trades. Such trained children, naturally, tend to be better 
citizens and better tradespeople. Special classes have been de- 
signed for children who are disinterested and unable to keep up 
with the work of the regular classes. Another type of school called 
the juvenile vocational school, designed to meet the needs of such 
children, is now being established in certain sections of the country. 
Not only will children who cannot get along well in the average 
public school attend these schools, but those who, due to economic 
pressure, must earn a living as soon as possible, will find a place to 
learn a trade. 

(6) Only the mentally, physically, and morally fit immigrants 
should be permitted to enter other countries. At present there 
are immigration laws restricting certain undesirable persons. Im- 
migrants are examined when they leave their own country, and 
at Ellis Island before* entering the United States. Care is taken 
to exclude all those with objectionable hereditary traits or with 


contagious diseases. But the effective enforcement of these laws 
is still a serious problem. 

Eugenics versus euthenics. Environment and heredity must 
go hand in hand if real racial progress is to be made. Bad en- 
vironment may harmfully affect good germ plasm. Frequency 
of crime is sometimes laid to environment rather than heredity. 
This is true to some extent, but heredity is usually responsible for 
choosing the environment. Intelligent people, as a rule, wish to 
live in good surroundings where they will meet people like them- 
selves. They try to meet and solve their problems. Subnormal 
people are frequently content with poor conditionSvof Kymg. Lack- 
ing normal will power and the ability to solve tnen problems in- 
telligently, they are dominated by the wrong influences. It is 
very difficult to dissociate, absolutely, heredity and environment. 
There is no question about the fact that eye color, hair color, and 
other structural characteristics are inherited, but there is little 
known about the inheritance of emotional characteristics. 

Inheritance of disease. It is a fairly well-established fact that 
no germ disease is inherited. In order to be inherited, a microor- 
ganism would have to become a part of a gene in the chromosome. 
Since this is impossible, germ diseases are not really inherited al- 
though infection may occur at birth, so that the effect on the new 
individual is the same as direct inheritance. In all probability, 
organic diseases, like malformations of glands, deafness due to 
structural defects in the ears, and organic heart disorders due to 
structural defects in the heart, do run through families. Weak- 
nesses in various organs may be inherited and result in tendencies 
or predispositions toward disease. 

Any disease of the mother, that gives off poisons that will circu- 
late in the blood may affect the germ cells and result in some ab- 
normal development of the unborn offspring. Such children may 
be born crippled, blind, deaf, or mute. Any disease of the mother 
that interferes with the nutrition of the unborn child may also 


cause developmental defects. For example, the offspring of a 
tubercular mother is likely to be delicate, lack resistance to dis- 
ease, or may show definite defects, because of faulty nutrition. 
The toxic and nutritional effects on the offspring are due to its 
environment. In these cases the environment is the mother's 
body. The relation is called intramaternal environment in con- 
trast with the environment of the child after it is born. This 
is called extramaternal environment. 

The relation of alcoholism to the offspring is not conclusively 
established. Experiments are constantly being conducted to 
determine whether alcohol may modify the germ cells or not. It 
is a fact that children of drunkards are frequently defective. This 
defectiveness may be (1) due to the fact that alcoholism is merely 
a symptom of a degenerate stock. In this case the children will 
be defective, not because their parents drank, but because their 
parents were defective. The parents' drinking is merely one of 
the symptoms of their defectiveness. (2) It may be that alcohol 
directly poisons the germ plasm. In this case parents of sound 
stock, who become addicted to alcoholism, will have defective off- 
spring. (3) It may be that the intemperate parents do not take 
adequate care of their children and this leads to the defects of the 
children. Whether the tendency for drinking alcoholic liquors 
is inherited, has not yet been definitely proved. 

Environment versus Heredity. One of the most interesting 
studies that has been conducted upon the relation of environment 
to heredity in the life of a child is the investigation of identical 
twins. Twins are thought to originate in the following way. When 
a fertilized egg divides into two cells, some mechanical or chemical 
difficulty may separate one cell from the other. Then each cell 
develops separately. The development of the two cells is exactly 
alike in every particular because each cell resulted from the 
division of the original cell. Such a development results in twins 
identical in sex, height, coloring, and almost every other particular. 



Investigators have found a pair of identical twins that had been 
separated at infancy and had been brought up in different envi- 

Journal of Heredity 
These identical twins were separated in their infancy. They were tested, after seventeen 
years of separation, and found to be very similar in physical and mental characteristics. 

ronments in different families in, approximately, the same social 
conditions. When they became adults, they were given intelligence 
tests and both were found to have practically the same intelligence 
quotients. They were successfully occupying professional posi- 
tions requiring about the same intelligence. The different envi- 
ronments had produced little change in the inherited mental 

Questions and Suggestions 

1. What is eugenics ? Give the history of the science of eugenics. 

2. What are three difficulties in investigating human heredity ? 

3. Discuss how histories were obtained from families of superior 
intelligence; from families of inferior intelligence. 

4. What is the relation of crime to heredity ? 

5. State two general methods of race improvement. 

6. Name seven euthenical measures that may be enforced ; discuss 
their importance. 

7. Discuss the topic "Environment versus Heredity." 



Jean Lamarck. 

uruwn Bros. 
Charles Darwin. 

How has organic evolution of plants and animals taken place f How 
old is the earth? How old is man? What are some of the evidences 
of evolution f 

All plants and animals of to-day are thought to be descendants 
of earlier and more primitive types. Organic evolution is the 
science that deals with the origins of species and the changes in 
them from generation to' generation. Evolutionists believe two 
things: (1) that individuals of the same species always vary; 
and, (2) that many of these new characteristics or variations are 
transmitted to succeeding generations. Heredity is, therefore, one 
of the cornerstones of evolution. 

History of evolution. Aristotle had an idea that there had been 
a gradual succession of living things from the simplest animal to 
man, but this supposition was unsupported by evidence or fact. 
He had seen the remains or parts of plants and animals in rock. 
To-day these are called fossils. He thought they were examples of 
spontaneous generation taking place in the depths of the earth 
and that such forms never had a chance to live on the surface. 
Nearly two thousand years later (1510), Leonardo da Vinci stated 
that fossils were the remains of former living animals. 

The Lamarckian theory of evolution. Jean de Lamarck (1744- 




' Am. Museum of Nat. History 

The skeleton of an amphibian dinosaur, the Brontosaurus, was unearthed in Wyoming in 
1898. The animals shown above have been restored by placing muscles and skin over the 
assembled skeletons. These animals probably ate soft plants and lived in shallow waters and 
are thought to have crawled out upon land to lay eggs. 

1829), a Frenchman, set forth his ideas on evolution in his book, 
La Philosophie Zoologique. He coined the expression use and dis- 
use to summarize his ideas of the causes of variation in species. 
He thought that organisms could adapt themselves to fit the envi- 
ronment. He supposed individuals acquired the characters they 
needed and these acquired characters were transmitted to their 
offspring. For example, he said that the original giraffe had a 
short neck. For some reason, it began to eat leaves from trees and 
was constantly stretching its neck to reach them. Consequently, 
the neck started to grow longer and the offspring were born with 
longer necks. According to Lamarck's theory, if a man developed 
his mind very carefully, his children would start with better minds. 
His theory has been generally discarded. Our present knowledge 



of heredity does not show that characters acquired in the life 
time of an individual organism are inherited. 

Recently, there has been a revival of interest on the part of cer- 
tain modern scientists in Lamarck's theory. They base their ideas 
on the supposition that over- or under-development of an organ 
produces hormones in different amounts, which may affect a gene 
in the germ plasm and cause variations. 

The Darwinian theory of evolution. The theory of natural 
selection was set forth in the book, Origin of Species, by Charles 
Darwin (1809-1882), but it was also formulated independently 
by Alfred Russel Wallace (1823-1913). Herbert Spencer (1820- 
1903) has exerted a profound influence upon thinking people 
through his philosophical writings on evolution. Darwin's theory 
is based largely upon deductions made from observations that he 

Am. Museum of Natural History 
Restoration is shown of a prehistoric reptile, Allosaurus, one of the largest carnivorous ani- 
mals that ever lived. It was forty-seven feet long with its head twenty feet above the ground 
when it stood upright. Below is the skeleton shown as unearthed. From its position, scientists 
think that it was feeding on one of the giant herbivorous dinosaurs just before its death. 


made after reading Malthus' Essay on Population and from mate- 
rial gathered during his trip around the world on a ship commis- 
sioned for, scientific exploration. It consists of the following 
principles. (1) Overproduction. More individuals are produced 
than can possibly reach maturity and reproduce themselves^ A 
plant commonly called the shepherd's purse may produce upon a 
single stalk as many as 64,000 seeds, and a tobacco plant may pro- 
duce 360,000 seeds annually. A single fern plant produces about 
fifty million spores a year. If all these spores matured; the United 
States would be covered with ferns in two years. A single salmon 
may lay 2,000,000 eggs, a female codfish 9,000,000 eggs, and a Vir- 
ginia oyster not less than 15,000,000 eggs. The sea would be a 
mass of writhing, struggling fish in three years if all survived. This 
overproduction leads to (2) a struggle for existence. Whenever 
there are abundant offspring, there must be ample food and room 
for life and development. Crowding makes the existence of indi- 
viduals a real contest or fight. A struggle ensues for obtaining 
food, for finding a mate, and for producing more young. All can- 
not survive. Those that do are better adapted to meet the 
conditions of their environment than the rest. It is a well-known 
fact that all the individuals of a species are not the same. Some 
are swift and some skillful, which help them to survive. These 
slight differences are known as (3) variations. These variations 
play a most important part in the struggle for existence. Each 
one that is swift of foot, strong, skillful, or protectively colored 
possesses a variation that fits him to his environment better than 
those that do not possess such a variation. Variations make 
animals unequal in the contest of life. There is a struggle for 
existence : some are killed off ; others, the fittest animals or 
plants, survive. Thus overproduction intensifies the struggle for 
existence ; this struggle results in (4) the survival of the fittest. 
Darwin's theory of selective survival is often called " natural 
selection." (5) Variations are usually inherited. Those slight 



variations which tend to fit a species into its environment are 
passed on to the offspring and thus a new species will eventually 

Am. Museum of Nat. History 

The earliest horse, the Eohippus, had four toes and the splint of the fifth toe on the fore- 
foot. The Mesohippus had three toes with a rudimentary fourth toe. In the Merychippus, 
only one toe reached the ground in walking. In the Hipparion one toe became greatly de- 
veloped and the other toes became more rudimentary. The Pleistocene horse, Equus, and 
the recent horse show this same characteristic. There were corresponding changes in the 
fore-feet, skulls and sizes of the various horses. 

arise. Since these desirable variations are preserved by heredity, 
each generation is better fitted to the environment than the pre- 
ceding one. And so Darwin believed that through the passing 


r?£ "ft ^"C 


Museum of Natural History 
From fossil evidences, the evolution of the horse has been reconstructed. There 

of years this slow accumulation of variations will lead to new 
species as well as to a great diversity in one species. 

There are a great many facts to support Darwin's theory of 
natural selection, although some objections are made to it. (1) 
Variations are frequently not inheritable, Darwin did not dis- 
tinguish between somatic and germinal variations. (2) The varia- 
tions frequently do not have anything to do with the fitness of the 
organism for its environment. (3) The struggle for existence 
does not necessarily weed out the unfit organisms. Frequently, 
the weeding out occurs before the organisms have grown sufficiently 
to have their characteristic differences appear. Plants and ani- 
mals are frequently killed off by agencies, forces, and accidents 
that do not discriminate between the fit and unfit. 

The de Vries theory of evolution. The theory of mutation was 
formulated by Hugo de Vries, a Dutch botanist, in 1904. He 
published his ideas in a book called Species and Varieties. Charles 
Darwin had collected many examples of organisms strikingly 
different from the other members in the species. These he called 
sports. He did not attach very much importance to them. Hugo 
de Vries based his theory of evolution on sports which he called 
mutants. Weismann's conclusions in regard to germ plasm had 
disproved the inheritance of acquired characters. He had claimed 
that modifications of the body or somatoplasm did not affect the 
germ plasm and therefore could not be inherited. This fitted in 
with the ideas of Hugo de Vries who had made direct observations 


Museum of Natural History 
has been a gradual increase in size from the most ancient to the present day horse. 

on the appearance of mutations among the plants in his gardens 
and greenhouses. He observed that mutants usually transmitted 
their peculiarities to their offspring. 

The theory of mutation differs from Darwin's theory of natural 
selection, in the following facts. (1) Among individuals of a 
species, different forms arise suddenly and independently, not 
gradually. These forms differ widely from their parents. The 
forms showing wide departures are mutations. In many cases these 
mutations are inherited. (2) Mutations may take place in any 
direction. They may or may not fit in with environment. They 
may or may not be favorable. The main thing is that some are 
capable of establishing themselves and some are not. (3) In gen- 
eral, the unfit mutants are likely to be eliminated through natural 
selection. (4) The fit mutants are likely to survive by natural 
selection. The mutationist does not believe that natural selection 
really starts the species. He believes that it controls the persist- 
ence or disappearance of the mutant. The keynote to the theory 
of mutations is that organisms must first appear with distinctive 
qualities that are inheritable in order to start a new species. 

There is practically no disagreement .among scientists concern- 
ing evidences that organic evolution has taken place. But, there 
is still much disagreement in determining which of the theories 
thus far formulated most nearly fits the facts. The de Vries 
theory of mutation is one that is generally accepted by many 

WH. FITZ. AD. BIO. — 25 




Part of a fossil backbone. 

Am. Museum of Nat. History 
Fossil footprints. 

The age of the earth. 
Before examining the 
evidences of evolution 
of present living 
things, it is necessary 
to understand some- 
thing about Paleon- 
tology, a science which 
deals with the life of 
past geological 
periods. Geological time includes all the time since the earth first 
started to be formed. Geologists have estimated the age of the 
earth by the relative age of various layers of rocks and metals. For 
example, the presence of a form of lead has been found in a Nor- 
wegian mineral composed chiefly of uranium. Assuming that the 
production of uranium ceased as soon as the earth and sun sepa- 
rated, geologists have agreed that this lead is about three billion 
years old. This was determined by estimating the length of time 
necessary for a small amount 
of metal uranium to break up 
into this form of lead. From 
this time and amount of metal, 
the age of the lead and, there- 
fore, the earth was calculated. 
The cliffs in a valley will 
show that rocks are laid in 
strata or layers. The succes- 
sive layers of the rock suggest 
that they were deposited one 
after another from the bottom 
upward. The top stratum is 

the mOSt recent One deposited. From drawing Museum Nat. Hist. 

-o i • j* • l i i p i A colossal, hornless rhinoceros of prehistoric 

.bach individual layer or rock days . 



From drawing Museum Nat. Hist. 
The shovel-tusked mastodon used 
its scooplike jaw to gather up vege- 
tation from the water. 

constitutes a record of the time when 
it was deposited. The thickness of 
the stratified rocks now exposed upon 
the earth surfaces of the continents is 
very great. Knowing how slowly sedi- 
ments accumulate upon the sea floor, 
the age of the earth must measure ap- 
proximately hundreds of millions of 
years. Determining the arrangement 
in which the strata were deposited is 
difficult, because, in different areas, 
different strata may be omitted for 
one reason or another. Consequently, 

the sequence is not always alike. In some areas a more recent rock 
deposit is exposed than in others. Sometimes the rock deposit 

may have been completely 
weathered or worn away. 
The formation of rocks differs 
in various parts of the country. 
Some rock was elevated from 
the sea and forms the land of 
to-day. This is known because 
it contains fossils of shells of 
animals that once lived in the 
sea. The flatness of the beds 
of rock seems to show that their 
movement from the sea was so 
uniform and gentle that their 
Original formation could not 
have been broken. 

The oldest historical records 
of Egypt or Babylon date back 
perhaps six or seven thousand 

From draining Museum Nat. Hist. 
Fossils of Titanotheres, prehistoric mammals, 
have been found in both Asia and America. 
At the time they lived, Asia and America were 
probably one continent joined where Behxing 
Strait is now located. 


*y° ^^ig SfnTi 

DawmANt XriFB 


Cenozoic &j?««e 

" Br "Eg ftamr 






"Or&ovieictn i 

ii(|i (, ''pli^il|llllillliii(/|[( 
lllll^i i ii i iii' ft liii ^ l UlilHHl 





11,000 000 



■46,000,000 ^. 


T te-e- ° V* » o* 1 <§ .' 





years. Recently, an earlier Egyptian civilization has been 
unearthed that dates back more than ten thousand years. The 
carvings left by prehistoric man in the caves of the Pyrenees are 
perhaps twice as old as the Egyptian culture just mentioned. 
According to the evidence that is now available, man has prob- 
ably existed only a few hundred thousand years. Beyond man 
stretches a chain of varied forms which can be arranged in pro- 
gression from the highly complex ones of to-day through simpler 
and simpler ones back to the simplest of all the one-celled plants 
and animals. 

Fossils. In the strata of rock are found fossils in all degrees of 
their original state of perfection, varying from trails, tracks, or 
imprints to perfectly preserved shells, wood, bones, and complete 
skeletons. As a rule, it is only the hard parts of the animals and 
plants which have been preserved from decomposition. Some- 
times the original organic substance is preserved, but more often 
it has been replaced by mineral matter. This slow process of 
replacement is known as petrification and the organism or the 
part of the organism is said to be petrified. In a skeleton of a 
prehistoric animal, particle by particle the lime was replaced by 
indestructible silica, the element found in stone, sand, and glass. 
Probably the most common forms of fossils are molds or casts. 
The dead animal or plant fell into soft mud in which it made an 
impression which was preserved long after the organic matter 
had been destroyed. Sometimes these molds harden or became 
filled with a substance which formed stone. 

Evidences of evolution. The organized data that support the 
development of the higher organisms from the lower ones are based 
on the following evidences: (1) geological evidences, (2) geo- 
graphical evidences, (3) morphological evidences, (4) vestigial 
evidences, and (5) embryological evidences. 

Geological evidences. The oldest known rocks appear to have 
no fossils in them. The next layer shows traces of life of the 


simplest character. The fossils of the most highly developed 
animal, so far discovered, found in the oldest rock (Paleozoic) 

Flying reptiles, the pterodactyls, were probably 
the ancestors of our modern birds. 

are those of an animal related to a crab, called the trilobite. As 
higher layers of rock are reached, fossils of more complex animals 
are found. These are different, but obviously related to the 
forms in the strata below. 

According to the present-day evidences, all life at an early period 
was in the water. The history of the development of life has 
been formulated from records made in rocks. It is thought that 
the most primitive forms probably appeared in the warm shallow 
waters of the flats between tides. First, there appeared plant 
forms, algae; later, animal forms, protozoa. There was no life 
on the land. The rocks and coarse soil were quite bare. Later, 
countless minute creatures appeared in the water. Their shells 
made up the great cliffs of chalk. 

After centuries had passed an organism appeared that had an 
organ for breathing air. It is thought that this form developed 
from the more primitive types. The first traces of the land ver- 
tebrates are the footprints of the amphibia. These are preserved 
in mud molds which have solidified into rock. 



Some amphibia are thought to have developed into animals, 
the reptiles, that breathed with lungs all their lives. The reptiles 
of the past are called dinosaurs. Those of the earlier Mesozoic 
period were small, but in the latter part of the period, they be- 
came more numerous and gigantic in size. The Brontosaurus 
was nearly seventy feet long. (See page 372.) The Allosaurus 
was a trifle smaller. It was a dragon-like creature that preyed 
on its larger but clumsier relatives. 

During this period, the pterodactyl, a huge bat-like animal, 
appeared. It glided through the air by means of folds of scaly 
skin extending from the fore-limbs to the side of the body. It 
had a large bill and a long tail. Its wing-spread was thirty feet. 
This is probably the animal that was transitional between birds 
and reptiles. The Archae- 
opterix was another an- 
cient birdlike form. It 
has long, grill-like, true 
feathers on its wings, a 
small jaw with teeth, and 
a vertebrated tail with 
feathers attached. There 
were claws on its wings. 
No transitional animal has 
been found showing how 
the scales of the reptiles 
developed into the feathers 
of the birds. 

While the birds were 
developing, a small, very 
inconspicuous group of 
animals made their ap- 
pearance. They had hair 
instead of scales, and had 

Am. Museum Nat. History 

The Archaeopteryx is the earliest known bird. 
Two fossil skeletons were found in Bavaria. The 
creature was about the size of a crow, covered with 
feathers as in modern birds. Unlike present-day 
birds, it had uniform teeth in both jaws. It probably 
used all four limbs in climbing trees. The clawed 
digits were adapted for this. It is probably an in- 
termediate form between reptiles and birds. 



a nourishing fluid for their young in certain glands of their skin. 
Their rate of metabolism was much higher than the reptiles. 

Am. Museum Nat. History 

The Paleozoic period is noted for its luxuriance of plant growth. Ferns, club mosses, and 
ferns related to the horsetails attained the size of trees and formed dense forests. Many 
cone-bearing trees are found, but none of the higher types of flowering plants. As the plants 
died and became part of the swamps, some unusual tremendous pressure transformed them 
into coal beds. 

Hence they are called warm-blooded. They retained the eggs 
inside their bodies until the young were almost fully developed, 
and supplied them with nourishment during development. These 
were the mammals. The platypus or duckbill of Australia is 
thought to be a transitional form between the egg-laying birds and 
the mammals. It is furry, has a bill like a duck, lays eggs, and 
feeds, its young with milk (page 513). The marsupials, such as 
the kangaroo, are somewhat transitional. The young are born 
before fully developed. They climb into a pouch in the abdo- 
men of the mother and complete their development there. From 
the early mammals of the Cenozoic era have developed the many 
species which dominate the earth to-day. Man belongs in this 
great group of mammals. 


Geographical evidence. It has been found that every group of 
organisms expands its range just as far as conditions permit. Re- 
gions in every way similar, so far as climate, soil, and other condi- 
tions are concerned, are inhabited by totally different plants and 
animals. Thus, the climate of Australia is not very different 
from some of North America, but the animals and plants living 
there naturally are not like those of North America. The same is 
true about other- similar regions. 

Regions that are very different are occupied by forms of plants 
and animals that are sufficiently similar to be considered of the 
same families. For example, goats and sheep, obviously related to 
each other, are found in tropical, temperate, arctic, and antarctic 
circles. They are thus living in varied surroundings. 

Darwin pointed out that where similar regions are occupied by 
different flora and fauna, these regions were always separated from 
each other by impassable barriers such as oceans, mountain 
ranges, and deserts. Thus Australia and America were always 
separated by the ocean, and land animals could not migrate from 
Australia to America. On the other hand, where similar plants 
and animals inhabit regions that are markedly different in their 
climate and soil, these regions are either connected directly, or 
show evidence of having been connected in the past. For ex- 
ample, the plants and animals found in oceanic islands are fre- 
quently related to the inhabitants of the nearest mainland. 
There is some evidence that tends to show that the islands Were 
a part of the mainland at one time. 

The Mongolian Expeditions. It has been known for some 
time that Behring Strait formerly existed as a land bridge con- 
necting America with Asia. It is thought that a similar connec- 
tion, by way of Greenland, connected America with Europe. It 
was observed that the animals of North America, Europe, and 
Asia north of the Himalaya Mountains were somewhat similar 
and it was thought that animals must have crossed these areas 





2. t^^^s vwSitcs 


xvWst, .vclncs *>vcmerus 

r*cr elites 







and mingled. For example, American camels and horses "may 
have migrated to Asia or vice versa. 

It was also known by 
geologists that the Gobi 
Desert, Mongolia, in Asia 
was elevated from the sea 
during the period of time 
when reptiles were abun- 
dant. It became dry 
land at that time and 
has remained dry ever 
since. The American Mu- 
seum of Natural History 
financed expeditions, 
headed by Roy Chapman 
Andrews (see frontis- 
piece), to Mongolia to 
investigate the desert for 
remains of reptiles. Since 
reptiles were the prede- 
cessors of man, it was 
hoped that a transitional 
form between the reptiles 
and man, or between the 
early mammals and man, 
would be unearthed. 
Because of climatic con- 
ditions, deserts are pecu- 
liarly fitted to preserve fossils. Few people have penetrated and 
lived in the desert, so fossils are more or less undisturbed. Asia 
was thought to be a dispersal center to Europe on one side and 
America on the other. These expeditions have met with the 
greatest success in unearthing remains of reptiles and early 



There seems to be a common plan of structure in the 
limbs of various vertebrates which points to a common 




mammals. Dinosaur eggs and dinosaur bones are there in abun- 
dance. The largest mammal ever found has just been un- 
earthed. Many of these fossils are on exhibition in the American 
Museum of Natural History in New York. 

Morphological evidences. There is great similarity in the 
structure of animals, particularly the vertebrates. It is thought 
that the bones which form the shoulder and hip girdle of man 
are analogous to the bones which support the front and rear fins 
of the fish. The bones of the arm and leg are variations of the 
bones in the fin. Between y^^^^^-r — feimxr-, 

the bones of the higher apes -"hm& limb 

and man there seems to be a 
difference in proportion only. 
There is also a muscle for 
muscle correspondence. 

Vestigial evidence. There 
are traces or rudiments of 
organs found in certain 
higher animals. These ves- 
tiges are no longer used. 
Probably the animal passed 
through a stage when it used 
such an organ. The horses 
of to-day have splints or use- 
less bones high upon either 
side of their hoofs. These 
are vestiges of toes. This is 
one of the evidences that 
the present one-toed horse 
developed or evolved from 
the ancient four-toed horse. 
Human beings have a great many vestiges. The appendix is 
large and performs an important digestive function in some ani- 


"Jpclvic Taones 

" fior-poise 

A striking evidence of descent is the rudimen- 
tary organs in higher animals. The snake shows a 
rudimentary pelvis and hind limbs. The nictitating 
membrane is still found among birds and reptiles. 
The porpoise shows vestigial pelvic bones. There 
are numerous other rudimentary organs in various 



mals ; in man, it is a vestige. The muscles of the ears of human 
beings are quite functionless although they are of value in aiding 
lower animals to hear. 

Embryological evidence. All animal embryos go through the 

^sb salamander* -Tortoise Chick sheep 

Vttfei'bifc "Viixmcxn. 

Embryos of various animals appear to go through very similar stages. Before differentia- 
tion has progressed very far, it would be very difficult to recognize a particular embryo. In the 
later stages of embryonic development, species take on special characteristics. 

blastula and gastrula stages. The most primitive many-celled 
animals we know are the sponges. They are simple gastrulae. 

The embryos of many vertebrates show similarities that are 
not noticed in the fully developed organisms. They all go 
through a similar early development. The nearer alike the adult 
organisms are the longer they will show similarities in their de- 
velopment. The higher vertebrates, the mammals, in their early 
stage of development, have gill openings similar to those found in 
fish. During embryological development, the diaphragm, which 
in the fishes shuts off the gill chamber from the rest of the body, 
in the human embryo moves well down into the body cavity. 

While the human embryo is at one stage in its development, it 
has a tail-like structure. The generalization of the development 


of embryos is known as the doctrine of recapitulation or the bio- 
genetic law. It states that the organism, in the course of its 
growth as an embryo, goes through stages similar to those through 
which the whole race has developed. This theory was first ex- 
pressed by Professor Haeckel, a German embryologist. Remember 
three words — ontogeny recapitulates phylogeny. Ontogeny is 
the history of an individual; recapitulates means repeats; phy- 
logeny, the history of the entire race or group. 

Evolution of plants. It is thought that plants, too, have gone 
through an evolutionary series, but because they have little in the 
way of skeletons to fossilize, less is known about their early his- 
tory than about animals. Early vegetation consisted of luxurious 
growths of mosses and ferns. One descendant of these primitive 
fern groups is called the giant Equisetum or horsetail. It is com- 
monly found growing along railroad embankments. This vegeta- 
tion died, decayed, and collected to a depth many feet in thickness. 
It became buried beneath newly deposited soil and was later 
pressed and heated by volcanic action. Ancient forms of bog 
mosses formed peat. Prehistoric ferns and allied plants formed the 
basis of our present-day coal deposits. Some fossils of the forms 
of vegetation then growing are preserved in the coal. The earlier 
plant forms had certain primitive forms of fibrovascular bundles. 
Many modern plants, though they have developed a more complex 
form, grow the primitive form first. Later came the seed-bearing 

. Questions and Suggestions 

1. What is evolution ? 

2. What are some of the ideas on evolution held by ancient scien- 

3. Discuss the use and disuse theory of the origin of species. 

4. Discuss the natural selection theory of the origin of species. 

5. Discuss the mutation theory of the origin of species. 

6. What practical difference does it make which theory of evolu- 
tion proves to be true ? 


7. How would Lamarck, Darwin, and de Vries explain the fact 
that horses in the north have longer hair than horses in the south ? 

8. How would Lamarck, Darwin, and de Vries explain the fact 
that the ancestors of giraffes had short necks and present-day giraffes 
have long necks ? 

9. Discuss the formation of the earth. 

10. How have scientists been able to determine, even approxi- 
mately, the age of the earth? 

1 1 . What is one of the estimates given of the age of the earth ? 

12. Discuss the formation of different types of fossils. 

13. Name five lines of evidence given to support the theory of 
organic evolution. 

14. Discuss the relation of the age and formation of strata of rocks 
to the fossils found in them. 

15. In outline form give the sequence of fossils found in rocks be- 
ginning with the fossils first found and going through those found in 
youngest rocks. What relation does this sequence bear to the sim- 
plicity and complexity of the animals ? 

16. Name three different types of mammals and give the distin- 
guishing characters of each type. 

• 17. Discuss the geographical evidences of evolution. 

18. What is the importance of the expeditions to the Mongolian 
desert ? 

19. Give examples of morphological evidences of evolution? 

20. What are vestigial evidences of evolution? Give examples. 

21. What are embryological evidences of evolution? Give ex- 
amples. * 

■ 22. Discuss the evolution of plants. 

23. Discuss coal formation. 

24. Give a report on the life and work of Lamarck, Charles Darwin, 
and de Vries. 

25. Look up and report on one of the Mongolian expeditions. 

Supplementary Readings 

Haupt, Arthur W., Fundamentals of Biology (McGraw-Hill Book Co.). 

Holmes, S. J., General Biology (Harcourt, Brace & Co.). 

Jewett, F. G., The Next Generation (Ginn & Co.). 

Osborn, Henry Fairfield, From the Greeks to Darwin (Charles Scribner's Sons) 




Photomicrograph of spirilla. Photomicrograph of cocci. 

What are parasitic bacteria f How can bacteria be studied? What 
conditions favor the growth of bacteria? What is the relation of bac- 
teria to food preservation ? 

Bacteria possess no chlorophyll. They cannot make their own 
food ; they are dependent upon other organisms for their nour- 
ishment. They, with many other plants lacking chlorophyll, be- 
long to a subdivision of Thallophyta. All bacteria are not harm- 
ful. Life on earth would probably cease were it not for the 
activities of certain bacteria. The disease-producing bacteria are 
known as pathogenic types. 

Structure of bacteria. When unstained, bacteria are colorless, 
transparent cells with comparatively thick cell walls. The nu- 
cleus is not organized, but nuclear material is scattered through 
the cytoplasm. Sometimes the cell wall absorbs water, becomes 
swollen, and forms a mucilaginous mass. The " mother of vine- 
gar " represents a mass of cells of this type. Another example is 
the mass of mucilaginous material that sometimes clogs the drain- 
pipe of the ice box. In other types, the wall becomes gelatinous 
and thick, and forms a capsule around the individual bacterium. 
In certain bacteria, small granules are found, which are probably 
reserve supplies of food. These particles absorb dyes readily and 
hold the stain very effectively. Some bacteria have one or more 
whiplike projections of protoplasm called flagella. They are the 




Rod-shaped bacteria, bacilli, sometimes occur singly. They may form strings and are then 
known as streptobacilli. They sometimes have projections of protoplasm, somewhat similar 
to cilia, called flagella. 

<S> <S> CO 
00 . OP 00 _ 

0D <P * CD 


CO ^ 

Spherical bacteria, cocci, may occur in pairs, diplococci; or in chains, streptococci; or in clus- 
ters, staphylococci. 





The spiral bacteria, spirilla, may not have flagella, or they may have them. These bacteria 
are always recognized by their twisted shape. 

motile bacteria and are able to move through the water by means 
of these structures. 

There are many different species of bacteria. Most of them 
may be grouped as one of three forms. These are the bacilli 
or rod-shaped bacteria, the cocci or spherical, and the spirilla or 
spiral. Bacteria vary greatly in size and shape within the same 
group, although they are all microscopic. The micron is the unit 
of measurement in microscopic work. It is about one-thousandth 



Photomicrograph of spirilla. 

For example, the pus in the 

of a millimeter in length or about one twenty-five thousandth 

of an inch. Bacteria usually vary from 0.5 to 5 microns in length. 
There is probably a very large 

group of disease-producing agents, 

which may or may not be bacteria, 

that have never been seen with the 

microscope. They can pass 

through ordinary bacteria-proof 

filters, and are known as filter 

passers or a filterable virus. These 

infectious microorganisms may be 

found in the secretion, the excre- 
tion, or blood of the body, and may 

be passed directly from one person 

to another, thus causing a disease. 

abscesses on the skin of a smallpox patient is a filterable virus. 

This material will generally produce smallpox if it is brought in 

contact with a well person. 
Bacteria are sometimes classified according to their relation to 

oxygen. Those that need free oxygen in order to live, are the 

aerobic bacteria, and those that live only in the absence of free 
oxygen and perish if exposed to it are the 
anaerobic bacteria. Certain forms of bac- 
teria of decay thrive without air. They 
obtain their oxygen by breaking down oxy- 
gen-containing compounds. 

Physiological functions of bacteria. No 
bacteria are completely independent. They 
lack chlorophyll and are, therefore, un- 
able to make their own food, but have to 
depend upon other organisms for it. Those 

bacteria that inhabit and obtain their food from living organisms, 

sometimes causing damage to those organisms, are the parasites. 

WH. PITZ. ad. bio. — 26 

Photomicrograph of strepto- 
bacilli enveloped in a muci- 
laginous sheath. 


They are not all necessarily harmful. Certain bacterial parasites 
are found in the intestinal tracts of animals, but they do not 
seem to produce any serious effects. The pathogenic bacteria 
are all parasites. All of these are harmful. 

Bacteria that inhabit and obtain their food from nonliving 
organic material are saprophytes. The bacteria that decay dead 
organisms are saprophytes. The bacteria that change alcohol 
to vinegar, sour milk, and ripen cheese are saprophytes. Practi- 
cally all of these are useful to man. 

When a parasite and its host both flourish, and each one pro- 
motes the growth of the other, their relation is one of mutual help- 
fulness and is known as symbiosis. Each member, the bacterium 
and its host, is known as a symbiont. For example, certain bac- 
teria, known as nitrogen-fixing bacteria, live in little nodules or 
swellings on the roots of clover plants. These bacteria take free 
nitrogen from the air and build it into nitrates which the plant 
can use. The clover plant uses some of these nitrates for making 
protein. At the same time the bacteria absorb sugar from the 
clover plant and use it for food. Neither organism suffers from 
this relation and each one benefits from it. 

Nutrition. All types of bacteria give off digestive juices or 
enzymes which digest the food upon which they are living. This 
food may be mineral nutrients, dead plant and animal tissue, or 
even living tissue. Digestion is external to the cell, not within 
the cell, as it is in the amoeba. For example, the tuberculosis 
bacilli digest certain cells of the body, then absorb the digested 
material. Practically all bacteria absorb protein from other 
organisms. The absorbed protein is either assimilated into new 
protoplasm or oxidized for the release of energy. As a result of 
assimilation, the bacteria grow, divide, and form groups or colonies. 

Reproduction. After the bacterium reaches its maximum size, 
it builds a cell wall across the middle of the cell and thus divides 
in half by fission. If conditions are favorable, certain bacteria 


may divide every twenty minutes. A single cell may produce mil- 
lions of cells within twenty-four hours. As bacteria divide and 
cling together, the mass of similar cells is 
known as a. colony. 

If conditions are unfavorable, many bac- 
teria will give off moisture, thus lessening 
their size, and surround themselves with a 
thick wall. In this form, the cell remains 
dormant until conditions are again favor- 
able for development. This is known as a 

r Different types of spores 

spore. All bacteria cannot form spores. are f0 . und amon s bacteria. 

Sometimes the spore forms 

Spore-formation in bacteria is not a type at one end of the ceil and 

. . * .. sometimes in the center. 

oi reproduction because no new cells are 

developed. It is a method by which the cell exists during un- 
favorable conditions. Spores may be dried without injury. Some 
spores may be heated to a high temperature, and the organism 
will still remain uninjured. 

Methods of identifying bacteria. Bacteria are so small that 
other methods of identification must sometimes be used besides 
their shape, size, and flagella. Some are recognized by their abil- 
ity to hold an acid stain, or to give particular color reactions 
with certain stains. Others are recognized by the changes they 
bring about in or on various substances on which they are grown. 
These substances are called media. The type of colony formed 
is also a means of identification. Some produce colonies with 
smooth, scalloped, or fringed edges. In some, the colonies are 
opaque; in others, they glisten. Different colonies of bacteria 
are characterized by different pigments. Some of the pigments 
are gray, yellow, pink, or brown. Some colonies develop on the 
surface of the media, others beneath the surface. The place and 
character of the spore formed are other means of identification. 
In some, the spore forms at one end of the cell ; in others, in the 
middle. A tetanus bacillus forms a spore at one end of the cell. 



It swells out and the bacillus looks like a drumstick. The diph- 
theria bacillus is characterized by granular particles which turn 
red with a certain stain and will not lose this stain. 

A method of identifying bacteria is through recognition of the types of colonies they form. 
Some colonies are translucent, others are opaque ; some have regular margins, others have 
irregular margins. One of the above plates has been exposed to bacteria, the other plate has 
not been opened and is sterile. This is called the control. 

Media for cultivation of bacteria. Beef broth is the principal 
medium used for the cultivation of bacteria. If a small quantity of 
the seaweed, agar, is added to this, a solid medium results. Some- 
times gelatin is used in place of agar, and prune juice, sugar 
solution, or blood instead of beef broth. The nutrient medium 
which will furnish the best nourishment for the particular bac- 
terium is selected. 

Bacteria are usually grown in Petri dishes or on agar slants in 
test tubes. The Petri dish was originally devised in 1887 by R. J. 
Petri in a Berlin laboratory. It really consists of two dishes, 
each one being a shallow glass saucer with a perpendicular rim. 
One fits rather snugly as a dust-proof cover over the other. 

First, the agar medium is boiled and filtered two or three times. 
The Petri dishes are thoroughly cleaned and sterilized. The hot 
sterile agar is then poured into the dishes. Great care is taken, 
in order to prevent any bacteria in the air from entering during 
the pouring or plating of the agar. 



In preparing agar slants, the test tubes must be plugged with 
sterile cotton and sterilized thoroughly. Then, the plug is re- 
moved, the sterile agar quickly poured in, and the plug put back 
in the mouth of the test tube. The test tubes are usually set 
obliquely for the agar to cool, so that, when firm, the surface of 
the media is slanting. Hence the term agar slant. This method 
gives more surface for the growth of bacteria. 

In order to introduce bacteria for cultivation into a Petri dish, 
the dish is uncovered and exposed to the air. After the expo- 
sure, the dish is kept closed. Bacteria may also be introduced 
with water, food, dust, or other foreign material. In introducing 
bacteria into the agar slant, the cotton plug is removed carefully 
so as not to get bacteria on it. The agar slant is then streaked 
or stuck with a needle infected with bacteria. 

Occurrence of bacteria. Bacteria are so extremely minute that 
they float in the air with the particles of dust. It is almost im- 
possible to find any air that does not contain them. Since this 

r " >*»*, 

One way of growing colonies of bacteria is on an agar 
slant preparation. The surface of the agar is streaked with 
the material containing the bacteria. The long slant gives 
considerable surface on which growth may take place. 

is the case, it is quite impossible for any material exposed to the 
air, for even a short time, to escape contamination from bacteria. 




Practically all bodies of water on the surface of the earth contain 
great numbers of bacteria. The numbers in different kinds of water 

•slant smzcccs 
B.coli tt.atththeriae 

•Stab CuYtures 

Two types of inoculations, smears and stabs, are made on slant cultures. After the media are 
incubated, the germs grow into colonies, each having a characteristic form and shape. 

vary according to the location of the water. In spring water, the 
number of bacteria is relatively small, but in water into which sew- 
age from cities drain, the number' is extremely large. Sometimes 
bacteria in water contaminated with sewage are disease producing. 
The soil that has been well cultivated is usually rich in bac- 
teria. The deeper layers of soil contain few or no bacteria. 
Where the soil is dry and sandy, there are relatively few bac- 
teria; where it is moist and loamy, they are abundant. They 
are found in great numbers around the bodies of dead animals or 
in soil that contains decaying roots of plants. 


Bacteria are probably found on all cooked foods which have, 
been exposed to the air, as well as on the surfaces of all fruits 
and vegetables. 

The relation of various conditions to the growth of bacteria. 
Most bacteria thrive best in darkness. Direct sunlight kills them 
after a few hours of exposure. Even spore forms may be killed by 
direct sunlight. The food of bacteria must be organic and must 
be slightly moist. The best temperature for bacterial growth on 
culture media is between 20°^ and 40° C, although bacterial life 
is possible at absolute temperature (— 273° C.) and at 160° C. 
The temperature varies with the particular type of organism. For 
example, the human tuberculosis bacillus grows best at blood 
heat, 37.5° C. ; the bird tuberculosis bacillus grows best at about 
42° C. Sudden changes in temperature are more or less detrimen- 
tal to bacteria. If changes are slow, the spore formers will have a 
chance to form their spores. Cold checks the growth of bacteria 
and continued freezing or alternate freezing and thawing may 
sometimes kill them. Different bacteria are killed at different 
temperatures. Active typhoid bacteria are killed when subjected 
to a temperature of 60° C. for thirty minutes. Ordinarily, all 
bacteria are killed at 100° C. Moist heat is found more effective 
for killing bacteria than dry heat. 

Methods of food preservation. Substances may be freed from 
bacteria, or the action of the bacteria on the substance may be 
materially decreased by depriving the organisms of some condi- 
tion that is necessary for their life or growth. Some of the 
methods of preserving foods against the action of bacteria are 
dehydration, refrigeration, canning, smoking, and addition of 

If a food is thoroughly dried, particularly by the sun, the bac- 
teria cannot thrive. The sun, in all probability, will kill them. 
Dryness is also an unfavorable condition for the growth of bac- 
teria. Refrigeration preserves foods because cold checks the 



A method of preserving foods is by sun-drying The picture shows plums exposed to sunlight 
until dry. This changes them to prunes and safeguards them from the attacks of bacteria. 

growth of most bacteria. In the refrigeration process, the flavor 
is not likely to be spoiled. It is an expensive method, however. 
Canning or preserving makes use of extreme heat to sterilize, then 
by placing the food in air-tight containers no new bacteria can 
enter. Smoke contains creosote, which is poisonous to bacteria, 
but, in small amounts, is not poisonous to people. Hence, smok- 
ing is a method of preserving food. Bacteria in an alkaline or 
acid solution are more easily killed than those in a neutral solu- 
tion. Housekeepers have found that canned fruits seldom spoil, 
but canned vegetables frequently cause trouble. Sometimes 
sugar, salt, and vinegar in quantity act as poisons to bacteria. 
They are not injurious to people. Producers frequently add pre- 
servatives such as benzoate of soda or mild acids to help kill the 
bacteria. Many of. these may be injurious. 

Problem. What is the number of bacteria found in the air in 'cari- 
ous places in the environment ? 

Prepare seven or eight Petri dishes of sterile agar media. 


I. Keep one Petri dish closed throughout the experiment. This is the con- 
trol and will serve as a comparison with the exposed dishes. 

II. Expose one dish of the agar media in a classroom at head leveU ex- 
pose one in the hallway through which many pupils pass ; one in the lunch 
room, one in the gymnasium, one in the street, and one in a theater. Cover 
all dishes immediately after exposure. 

A. Incubate the dishes between 30° to 40° C. until colonies appear on 
the surfaces. 

B. Compare the dishes with the control. 

C. Which dishes show the greater number of colonies ? 

D. Which dishes show the greater number of different kinds of colonies ? 

E. What seems to be the relation between dust and bacteria ? 

Problem. What is the bacterial content of different kinds of milk f * 

I Put a couple of drops of certified milk in a Petri dish containing 
sterile agar. Cover the dish immediately and permit the milk to completely 
cover the agar. 

II. Repeat the experiment for grade A and grade B milk. 

III. Incubate the dishes for twenty-four hours at between 30° and 40° C- 

IV. Which milk shows the greater number of colonies ? 

V. Which milk shows the greater number of kinds of colonies ? 

VI. What is the danger of having a great number of kinds of colonies ? 

VII. In selecting milk, state anything else, besides bacterial content, that 
must be considered. 

VIII. State one possible reason for using pasteurized milk and one reason 

for using certified milk. 

Problem. What is the effect of various antiseptics on the growth of 

bacteria f 

Expose each of five dishes of sterile agar media to dusty air in order to 
inoculate them or introduce germs into them. 

I. Cover one and keep it closed throughout the experiment. 

II. Pour a little boric acid into dish number 2. Cover it and tip the dish 
repeatedly until the boric acid completely covers the surface of the agar. Be 
sure not to use any more than just enough to cover the agar. 

III. Repeat the experiment, using iodine, salt solution, and mercurochrome 
in each of the other three dishes. 

* All cities do not grade milk as A, B, and certified. If different forms of grading 
milk are used in your community, use those in performing this experiment. 



IV. Incubate the six dishes for twenty-four hours. 

V. Make repeated daily observations. 

A. Which material used seems to be of least use in checking the 
growth of bacteria ? 

1. Compare the growth of colonies in this dish with your control. 

B. Give the effects of each of the other solutions on the growth of 

C. Which antiseptics might be unwise to use on delicate lining mem- 
branes such as those in the throat, nose, and eye? 

VI. The experiment may be repeated to test the results of various mouth 

VII. Antiseptics should be used with great discretion. Some of them kill 
bacteria rather than check their growth. They are called germicides. Those 
that check the growth of bacteria are the true antiseptics. Germicides may kill 
the tissues as well as the bacteria. This, in many cases, will check healing. 

Questions and Suggestions 

1. Describe the structure of bacteria. 

2. Classify bacteria according to their shape. Give some in- 
dividual variations of each type. 

3. What are aerobic and anaerobic bacteria? 

4. Discuss three different types of nutrition found among bacteria. 
Give an example of each type. 

5. Discuss reproduction and spore-formation. 

6. Name five methods used in the identification of bacteria. 

7. What is the importance of agar ? 

8. Discuss the sterilization of agar and of Petri dishes. Discuss the 
methods of inoculation, and conditions for the cultivation of bacteria 

9. Discuss favorable conditions for the growth of bacteria. Which 
of these conditions are found in the human body ? 

10. Under what conditions will food spoil ? 

11. Name some conditions unfavorable for the growth of bacteria. 

12. Give in the form of an outline the method of preserving certain 
foods from the activities of bacteria, and the resulting conditions that 
are unfavorable for their growth. 

13. Discuss the relative number of bacteria in different types of air. 

14. Discuss the bacterial content of different types of milk. 

15. What is the relation of different antiseptics to the growth of 
bacteria ? 



V lactik J 
* eccidL f 






moth er of vfoiegor 


« ©i> 


Curdling of milk. 

Souring of fruit juices. 

Why does milk turn sourf What makes sweet cider turn into 
vinegar t Why will the dead body of an animal putrefy f What is 
the importance of the rotation of crops f 

Bacteria which are of value to man may be grouped into 
three classes : (1) those necessary for the preparation of certain 
foods; (2) those aiding industries; and (3) those useful in 

Bacteria in food preparation. Certain bacteria in milk change 
the milk sugar, lactose, to lactic acid. The production of this 
acid coagulates or curdles the protein in milk. This process of 
acid-formation and protein-coagulation is called souring. When 
the acid reaches a certain concentration, the process ceases. The 
presence of lactic acid in cream increases the yield of butter and 
improves the flavor. Lactic-acid bacteria are necessary for the 
production of sour-milk cheeses such as Swiss, Edam, and Ca- 
membert. The flavor of these cheeses is partly due to the lactic- 
acid fermentation and partly to mold activity. 

Acetic-acid bacteria convert alcohol into vinegar. Yeasts first 
attack the sugar of fruits or grains and convert it into alcohol, then 
the acetic-acid bacteria attack the alcohol and change it to 
vinegar. This vinegar is useful in preserving foods because 
bacteria of decay cannot work in a ^strong acid medium. 



If cabbage is finely chopped, salted, and packed tightly in 
jars or barrels, it will undergo a chemical change. The salt will 

foool fooa. 





acicl coocste toxin 

When bacteria absorb and use food, they give off acid wastes. The wastes of disease- 
producing bacteria are called toxins. 

extract from the cabbage the juice which is a good medium for 
the growth of lactic-acid bacteria. This will attack the tissues of 
the cabbage, changing it to sauerkraut. Meat is made tender 
by the action of bacteria. When meat is fresh, that is, soon 
after the animal is killed, it is tough and more or less tasteless. 
Bacteria attack the muscles and connective tissue, loosen the 
fibers, and give the meat a taste. Meat is usually kept for some 
time to permit this bacterial attack. This is the beginning of the 
decay process. The process must not go too far or products that 
are objectionable are formed, and the meat is said to be tainted. 

Ensilage is prepared for stock by packing finely chopped fodder 
in a silo. Bacteria and enzymes will attack the tissues of the 
fodder, causing it to change in appearance, flavor, and nutritive 

Bacteria in other industries. Sponges are animals. The fairly 
hard commercial sponge is really the skeleton of the animal. This 
skeleton is composed of substances secreted by the cells of the 
animal. The sponges of commerce are prepared by cutting their 
attachment to the sea floor. The sponges are spread out on the 
seashore and bacteria destroy the soft organic parts, leaving the 
fibrous, horny framework or skeleton. This process is known as 
curing. The exoskeletons are then thoroughly washed and 
cleaned and sold for commercial uses. 



There are many different 
bacteria which grow in milk. 
A group attacks milk sugar 
and produces lactic acid, 

A similar process takes place in preparing linen fibers. Linen 

comes from the flax plant. If the flax is cut and thrown into pits 

and kept damp, certain bacteria will decay 

the cementing materials which hold the 

tough, strong fibers together. These fibers, 

when separated, are used for the manufac- 
ture of linen. This process of obtaining the 

fibers of flax is known as retting or rotting. 

There is an artificial process of retting which 

is not as successful as the natural water 

process. The natural process is used in 

Ireland and produces a fine grade of linen. which results m - souring. 

The artificial process, used in the United States, consists of an 

acid treatment for loosening the fibers. It is much quicker than 

the natural method, but less perfect, since the acid may roughen 

the flax fibers. 

Bacteria are valuable in curing tobacco. The tobacco stalks 

with the leaves are piled into great heaps or hung from racks and 

allowed to sweat and then ferment at a fairly low temperature. 

This gives to tobacco its special flavor. 

In tanning leather, the hides are soaked, scraped, and limed or 

treated with acids to remove the hairs. The lime is removed, 
and the hides are put into solutions of tan- 
bark. During these processes, certain bac- 
terial fermentations take place, which make 
'the leather soft and pliable. 

Bacteria in agriculture. Large quantities 
of the nitrates from the soil are built into 
proteins and protoplasm by the plants, 
in fruit juices bacteria When these plants are removed, they take 

change alcohol to acetic c " 

a«d. with them the nitrogen in the form of 

protein and protoplasm. The nitrogen of the soil would be 
exhausted in a comparatively short time if there were no ways 


of replacing or renewing it. The same is true of sulphur and 

Bacteria of decay are essential in farming. They bring about 
the decomposition of complex organic compounds into simpler 
ones. When this is accompanied by offensive odors, the process 
is known as putrefaction. The complex proteins and protoplasm 
of the plant or animal contain nitrogen. When a plant or animal 
dies, the bacteria of decay attack these nitrogen-containing com- 
pounds and break them down into simpler substances. One of 
these is a nitrogenous material, ammonia ; another substance con- 
tains sulphur. Phosphorus and the other elements present may 
be liberated, similarly. The decay process also sets free carbon 
dioxide and water. Nitrogenous wastes of animals are usually 
changed into ammonia by the action of the bacteria of decay. 

Nitrification. Certain bacteria called the nitrifying bacteria 
take the ammonia formed by the bacteria of decay and change it 
into nitrates which the plants can utilize for further protein- 
making. This process is called nitrification. Ammonia is a gas, 
and would escape into the atmosphere were it not for the nitrify- 
ing bacteria. Nitrite bacteria first convert ammonia into nitrites, 
compounds formed by the union of ammonia with oxygen. Then 
other organisms cause the nitrites to take up more oxygen and 
form nitrates which are stable compounds and can dissolve in 
the soil water. Nitrite and nitrate bacteria are always found 
together. They work best in alkaline soils. If a sample of soil 
is heated and thus sterilized, the action does not take place. 
This indicates clearly that the process is a bacterial one and not 
simply a chemical one. Nitrification takes place only in soil 
that is well aerated and well drained. The drainage carries off the 
acids that might interfere with the process. Aeration is necessary 
because there must be enough oxygen to combine with the ammonia 
to form the nitrites and the nitrates. Earth worms aid in this 
process by constantly working through the soil. This permits the 



The soil bacteria are irreg- 
ular-shaped organisms. 

entrance of air. Lime is sometimes added 

to soil to neutralize its acidity so that the 

nitrifying activities may be increased. 

Denitrification. If soil is poorly drained, 

poorly aerated, and contains fresh organic 

matter, denitrifying bacteria thrive. They 

convert the ammonia, formed in the decay 

process, into free nitrogen. The free nitrogen 

then escapes into the air and is lost to the 

plants. The denitrifying bacteria can also break down nitrates into 

nitrites, then into ammo- 
nia, and finally into free 
nitrogen. Soil should 
not be covered thickly 
with unrotted manure as 
the activity of these bac- 
teria are then promoted. 
From the point of view of 
conserving soil fertility, 
the denitrifying bacteria 
are undesirable. Certain 
other bacteria are able, 
however, to take free 
nitrogen from the air 
and again change it into 
a form in which it can be 
used. These are called 
the nitrogen-fixing bac- 

Nitrogen-fixation. The 
nitrogen-fixing bacteria 

Nitrogen-fixing bacteria form nodules or small swellings , , , , ,. 

on the roots of pod-bearing plants. The Countless bac- have already been (lis- 
teria in these nodules fix free nitrogen of the air into a i • x l 

usable form, nitrates. CUSSed in the preVlOUS 



chapter. When a pod-bearing plant, such as the clover, alfalfa, 
bean, or pea, is young, its roots are attacked by the nitrogen-fixing 

bacteria found in the soil. They 
penetrate the roots through the deli- 
cate roothairs and establish them- 
selves in the outer layer of the root 
cells. The root accommodates them 
by building more cells in that region, 
forming little nodules or tubercles. 
In these nodules, the nitrogen-fixing 
bacteria multiply. They take the 
free nitrogen from the air which 
permeates the soil, and build it into 
nitrites which are later converted 
to nitrates. When the roots of these 
plants are plowed under, they decay, 
and the nitrates are liberated into 
the soil. Soil may be inoculated with 
cultures of nodule bacteria. A crop 
of clover or alfalfa plowed under 
supplies the soil with about 100 
pounds of nitrogen to the acre. Such 
a crop is as valuable as many loads 
of manure. A good crop of corn or 
wheat will take from 50 to 75 
pounds of nitrogen per acre from soil. There are certain free- 
living soil bacteria which build nitrogen into nitrates when con- 
ditions are favorable. The result of the activity of these organ- 
isms is not unlike the nitrates formed by nitrogen-fixing bacteria. 
But they differ from the nitrogen-fixing bacteria in that they do 
not need roots of plants for their homes. 

Lightning and similar electric discharges in the air unite some free 
nitrogen with oxygen to form nitrates. These are washed from the 

The value of nitrogen-fixing bacteria 
was demonstrated in the above experi- 
ment. When the roots of the plants 
were examined, those on the left had 
numerous well-developed tubercles ; 
those on the right had no tubercles. 
They were both watered with a nutrient 
solution containing all the necessary 
nutrients but nitrogen. Explain the 
relation of the tubercles to the growth 
of the plant. 



air by rain and thus reach the soil. Exceedingly small quantities 
of nitrates are formed in nature in this way. Commercial processes 
of building nitrogen into 
nitrates is now being con- 
ducted in several sections 
of the country. Com- 
mercial nitrates are 
generally used for ferti- 
lizers. One of these 
plants is at Muscle 
Shoals, Alabama. The 
excellent water-power 
facilities of that location 
supply the necessary 
energy for the project. 

Rotation of crops. 
Crops are rotated, that 
is, one crop succeeds a 
different kind in the 

same field year after year. The reasons for crop rotation are as 
follows : (1) Plants use up varying amounts of the different min- 
eral matters in the soil. One crop might need a quantity of 
calcium salts but not much iron. Another crop will require 
considerable iron but fewer sulphates. If one crop is planted year 
after year in the same plot of land, that land will grow poor in one 
or more mineral salts and the quality of the crops will be greatly 
impaired unless commercial fertilizers are used. Where rotation 
of crops is practiced, the same soil can be used for years without 
adding fertilizer. (2) Plants are subject to diseases caused by 
bacteria and other fungi. If only one crop is planted, the soil 
may become infected with spores of disease-producing organ- 
isms. Another crop probably would not be affected by these 
spores. For example, corn smut will not injure potatoes; po- 

WH. FITZ. AD. BIO. — 27 

There is a continual building and destruction of carbon 
compounds. This is described diagrammatically in the 
carbon cycle. 



tato blight will not affect wheat. Rotation of crops also kills 
insect pests that live only on a certain plant. (3) The un- 
gathered roots and stalks of crops remain in the ground, 
decay, and produce organic acids. These acids are sometimes 
injurious to the plant producing them, but not to other plants. 
Hence, the crops should be changed. Bone meal or lime is added 
to neutralize these acids. Each commercial fertilizer used, how- 
ever, adds that much to the farmer's expense. (4) Almost all 
crops remove great quantities of nitrates from the soil. These may 


A number of different bacteria aid in transforming nitrogen into a form which plants can 
use. There is a constant renewal of nitrogen in the soil. 

be restored in a variety of ways. Animal waste, manure, may be 
spread over soil and allowed to decay. This increases the nitrogen 


content. Any organic material which decays will accomplish the 
same thing. Many commercial fertilizers are made from guano, 

cccrbohyclrates^^- ^ carboiv clio*i3e.> > ^ "*\^^" 03tf y^ en - 

proteins_ v / \" Ur, f_T. / ^^-nilrat^S 

-Salts \, / 

There is an interdependence between green plants and animals. Animals can make use of 
the oxygen excreted by green plants. These in turn, can make use of carbon dioxide, water, 
and possibly urea excreted by animals. 

bird waste. Refuse from abattoirs, and meat and fish canneries, 
or specially prepared mixtures of chemical compounds, may be 
purchased and plowed into the soil. The land may be allowed 
to lie fallow, that is, unused for a season or so. Certain minerals 
in the ground may break down in fallow fields and thus restore 
the usable mineral elements. A leguminous crop, such as peas, 
beans, or alfalfa, may be planted, allowed to grow, and marketed. 
At the same time, nitrates are restored to the soil in which' they grow. 
Soil conservation. If the soil is kept in good condition, nitrates, 
sulphates, and phosphates are constantly renewed as they are 
removed. The passage, use, and return of these materials consti- 
tute a cycle as shown in the diagram. Were it not for the action 
of bacteria in the soil, all vegetation on the earth would cease. 
Soil fertility is primarily a bacterial activity. Bacteria are com- 
monly thought of as being particularly injurious. In reality, the 
beneficial effects of bacteria far outweigh the injurious effects in 
many ways. 

Questions and Suggestions 

1. Using the following topics, make out a tabular outline of the 
relation of bacteria to food preparation. 

A. Name of bacterium. 

B. Material attacked. 


C. Material produced. 

D. Commercial use of material produced. 

2. Make a library report on the tanning of leather. 
• 3. What is meant by soil exhaustion and soil renewal? 

4. What is the importance of the decay process to agriculture ? 

5. Explain nitrification in detail. 

6. Discuss denitrification. 

7. Discuss nitrogen-fixation. Give three different ways of fixing 

8. What is the importance of rotating crops ? Give at least four 
reasons for rotating crops. 

9. Mention four different facts that must be considered in culti- 
vating soil. 

10. Make out an original carbon and nitrogen cycle. 

11. Do farmers have scientific knowledge about bacteria or do they 
depend upon their experience or on hearsay in caring for the soil ? 

12. Does the government make any effort to give farmers scientific 
instruction in soil and crop improvement ? 

13. Discuss a balanced aquarium. 

Supplementary Readings 

Gager, C. S., General Botany (P. Blakiston's Son & Co.). 
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.). 
Holman, R. M., & Robbins, W. W. A Textbook of General Botany (John 
Wiley & Sons, Inc.). 


^^- ' | 

& Er 

jj¥ra^ ■Kjt^tfi 





\" w """1^8 


Ewing Galloway 
Push ball. 

Ewing Galloway 
Outdoor swimming pool. 

Should people learn about diseases? Is longevity more or less con- 
trollable? Has community or individual control of disease been more 

Some people object to studying disease because they worry about 
each disease studied, fearing that they have it or may contract it. 
Education in health and disease should enable people to exercise 
an intelligent attitude toward disease, to practice ways of prevent- 
ing disease, and to learn how to conquer and control disease. 

Disease and health. The best way of preventing disease is to 
stay in good health. Some people feel that they are in a healthy 
condition if no disease is present. Even though there is no actual 
impairment of bodily functions, certain organs may not be in nor- 
mal condition, consequently, health is not necessarily a lack of dis- 
ease. Nor is the feeling of being well an infallible measure of the 
degree of health. Frequently people feel very ill when the actual 
illness is slight; on the other hand, people may have only a slight 
feeling of discomfort and yet have a serious organic disorder. An 
adequate measure of health is an annual physical examination. 
If people are examined thoroughly every year, beginning symptoms 
may often be detected before a disease has advanced to a serious 
degree. Health examinations are just as important for well as for 
sick people. In disease-control, prevention is far more important 




Am. Museum Nat. Hist. 

Bacteriological laboratories contain elaborate equipment. Can you identify the microscope, 

Petri dishes, agar slants in test tubes, staining fluids for bacteria, distilled water in flask 

for washing off excess stain, and the Bunsen burner ? Can you give the use of each article in 

working with bacteria ? 

than attempts to cure disease. Each illness, no matter how slight, 
is likely to lower the resistance of the person just that much. 

Health and longevity. Another misconception of health is that 
it is identified by length of life or longevity. This; too, is 
probably a fallacy. Some delicate people receive medical treat- 
ment all their lives, and, through care, live a long time, although 
they never really have good health. On the other hand, people 
in perfect condition may meet with accidents which will cut short 
the span of their lives. 

Health and adaptability. Positively speaking, health is merely 
the adaptability of the organism to meet a variety of situations. To 
be healthy, an organism must be able to make rapid and proper 
adjustment to every situation. For example, normal heart muscles 
thicken to accommodate the heart to unusual conditions. A dis- 
eased heart will not do this, consequently, discomfort results. Ac- 
quiring resistance to certain diseases is a process of adaptation. All 



people do not have an equal resistance. Those who have not 
must learn how to acquire it. Therefore, education along 
these lines is necessary. People must be taught hygienic living 
so that they may adapt themselves properly to changes of tem- 
perature, work, and food. Many diseases may be avoided by 
correcting improper habits of living and certain physical defects. 
Health and education. Health is one of the main objectives of 
education. Unless the body can adequately adapt itself to chang- 
ing conditions in life, the person is inefficient. In the past, undue 
emphasis has probably been placed on defects. Open-air classes 
were established for cardiac, anaemic, and tubercular children. 
Nutrition classes were established for malnutrition cases. Each 
year the health of some children was built up in these classes to 
such an extent that the children were able to continue in regular 
classes. Each year new cases would appear in regular classes which 
would have to be sent to these special classes. Nutrition classes are 

Underwood and Underwood 
Play in the sunlight is the heritage of childhood. It leads to a proper physical development 
and builds a healthy nervous system. 



necessary, but if the entire school were properly educated in 
health habits, and if there were a check to see that these habits, 

A properly cared for set of teeth is the result of frequent expert inspection. In certain schools, 
oral hygienists make surveys of mouths and suggest dental treatment when necessary. 

once taught, were enforced in the home and community, there 
would not be so many anaemic, cardiac, and tubercular cases. 
In order to show how much education could accomplish in disease, 
the Metropolitan Life Insurance Company and the National Tu- 
berculosis Association conducted an experiment at Framingham, 
Massachusetts. A campaign of education was carried on so suc- 
cessfully that tuberculosis was reduced 69 per cent in that com- 
munity within ten years. 

Effective education in health is evidently needed. This is par- 
ticularly pertinent when we consider that the statistics, prepared 
by General Crowder of the United States Army, showed that 
33 per cent of the United States soldiers in the World War were 



unfit for front-line duty. They had been out of school a very 
short time, but, evidently, had received very little, if any, instruc- 
tion in health. 

Science and health. In the Report on National Vitality, issued 
by President Roosevelt's Conservation Commission on National 
Vitality, it was claimed that the reasonable application of scientific 
knowledge would add at least fifteen years to the average lifetime. 
It stated that at least 40 per cent of American mortality was pre- 
ventable or postponable. There are probably always three mil- 
lion people ill in this country at one time. About 50 per cent 
of this illness is probably preventable. This report was issued 
in 1909. The expectation of life has gone up since that time from, 
approximately, forty-five years to fifty-five years, according to the 
figures of the Life Extension Institute. 

Underwood & Underwood 
Health is more often a matter of prevention than cure. In baby clinics, nurses weigh, measure, 
and make various examinations of babies to make sure that they are in good health. 

Along with the diseases that have been partially or entirely con- 
trolled through scientific investigation and health education, there 
has been a big drop in mortality. The deaths from typhoid fever 



have been reduced 75 per cent, and typhoid is generally termed a 
vanishing disease. The death rate of tuberculosis has been reduced 

about 50 per cent. Diph- 
theria is now preventable 
and is becoming infre- 
quent. In states where 
prophylactic measures 
are used, the Board of 
Health expects to have 
the disease under com- 
plete control by 1930. 
The diseases that may 
be considered as largely 
under individual control 
show increasing death 
rates. Heart conditions, 
diabetes; and kidney 
diseases are examples of 
these. They are, to 
some extent, dependent upon a person's habits of living. 

It is an accepted fact that the general life expectancy span 
at birth is increased. Believing that every one has the right to 
live, science has enabled us to bolster up the weakling at birth 
and all along the way — but eventually he drops out, the fight is 
too great. Science has decreased the infant mortality rate only 
to have the weaker ones die at a younger age than those with a 
stronger physical start. If life is to be lengthened at the other 
end, every individual must take more interest in, and insist on 
living hygienically. Much is still to be done. Ten years could 
be added to the expectation of life if all sections of the popu- 
lation could live under the same favorable conditions that are 
enjoyed by groups and communities where the death rates are 
unusually low. Individuals must be educated to have an intelli- 

Underwood & Underwood 
A physical examination includes the taking of one's pulse 
rate and temperature. 


gent knowledge of disease and understand its prevention. There 
are still too many defects such as mouth infection, tonsil infec- 
tion, overweight, underweight, foot defects, and visual defects. 
If all people had an annual health examination, many diseases 
would be prevented. Disease prevention should be an incentive 
for all people since it will reflect in the substantial gains in the 
vitality of the nation. In the previous chapters, suggestions 
concerning diets, sunlight, exercise, rest, and mental relaxation 
have been given. In subsequent chapters methods of avoiding 
actual diseases will be discussed. 

The measurement of health. A test to show whether one's 
personal habits are hygienic is the Payne " Habits and Practices 
in Accident Prevention and Health " given in the Appendix. A 
high school student should score at least 355 under A, 75 in the 
items under B, and 70 in the items under C. The points total 500. 

Questions and Suggestions 

1. What is a popular objection to the study of disease ? 

2. Name three popular misconceptions of health. Discuss the 
fallacy in each of them. 

3. Give a scientific definition of health. 

4. How may health be attained ? 

5. What can be accomplished by education in health ? 

6. Why do we find a larger reduction in the diseases that a com- 
munity can control, than in those that an individual must control ? 
Why is this true ? 

7. Discuss your ideas on an annual health examination. 

8. Give some examples of adaptations of the organism to changing 

9. Discuss your ideas on the scoring of health practices. 

" 10. Score your habits and practices, as suggested in the test in the 
Appendix, on a separate piece of paper. Add the score and see how 
closely you approximate hygienic living. 




Edward Jenner. 

Keystone View Co. 
Tribute to Jenner and 

Has smallpox ever been epidemic? Is inoculation for smallpox a 
new method of treatment f How did vaccination first start? What 
effect has vaccination had on the mortality from smallpox? 

History of smallpox. Smallpox was known in China many cen- 
turies before the Christian era. It also existed in India, Arabia, 
Ethiopia, and neighboring countries. It spread through Europe 
during the Crusades. The first epidemic of smallpox in Europe 
took place in the latter part of the sixteenth century. For centu- 
ries, it was estimated that ten out of every hundred deaths were due 
to smallpox. More than half the people in Europe were scarred and 
disfigured by the disease. It is probable that at least 60^000,000 
people died from smallpox during the eighteenth century. 

The disease was first brought into America by the Spaniards 
about 1515. Within a short period, three and a half million people 
in Mexico died of it. Probably half of the American Indians died 
during various epidemics of smallpox. Boston has had six epi- 
demics ; in the last one, 1752, there were 5989 smallpox victims 
out of a population of over 15,000 ; of these, 894 died. 

History of inoculation against smallpox. Inoculation first origi- 
nated in the Orient, hundreds of years ago. The people would 
introduce into a cut or scratch of a well person, the pus or scab 



from smallpox patients. This, in many cases, brought about 
protection against the disease. The practice of inoculation was 
carried into Europe by way of Asia, Africa, and Constantinople. 
In Turkey, certain old women took pus from the pustules of per- 
sons suffering from smallpox and inoculated it into the veins, of 
well people. 

In 1717, Lady Mary Montague, while traveling in Turkey, had 
her little son inoculated with smallpox, and he did not contract 
the disease. Through this incident, the idea of inoculation as a 
preventative was introduced into England, although many people 
were afraid of its results. Several years later, authorities offered 
a number of criminals confined in the Newgate Prison, England, 
their freedom, if they would submit to an inoculation against 
smallpox. They did so, the results were satisfactory, and they 
received their freedom. After this, the practice gained steadily 
in England. When a person was to be inoculated, he was usu- 
ally kept on a light diet for about six weeks. He was then 
purged and bled to make sure that his body was in good condi- 
tion. Then he was inoculated with smallpox. Pus was taken 
from the pustules of a person with a mild case of smallpox and 
placed in several scratches made on the body of the patient. 
This usually resulted in a mild form of smallpox to the person 
treated, but was supposed to protect him against a very severe 
form. This method of inoculation was somewhat dangerous 
to a community, in as much as new cases of smallpox, however 
mild, were likely to develop. 

History of vaccination. It had been a belief, for an unknown 
length of time, in rural districts, that people who had contracted 
cowpox, a disease of cows, did not take smallpox. A farmer 
named Benjamin Jesty, in 1774, took some pus from the sore of a 
cow with cowpox and inoculated his wife and children. This 
made them immune to smallpox infection. But Jesty's experi- 
ment never became generally known. It was Edward Jenner 



(1749-1823) of England, who first made known the idea of vac- 
cination. The germ theory of disease had not yet been pre- 


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In 1874 vaccination was introduced into Prussia. Note the decrease in smallpox in the 
following year. Vaccination is not compulsory in Austria. The above graphs indicate a direct 
relation between the number of smallpox cases and compulsory vaccination. 

sented by Pasteur. Jenner, however, collected data from the 
people who had had cowpox, and afterward had resisted small- 
pox infections. He began the scientific investigation of inocu- 
lation. A dairy maid on a certain farm contracted cowpox. 
Jenner took some pus from a sore on her hand and inoculated a 
little boy with it. The boy became slightly ill, but soon recov- 
ered. Later the boy was exposed to smallpox and even inocu- 
lated with smallpox virus, but he did not contract the disease. 
Evidently the cowpox infection had given him a protection 
against smallpox. Jenner made many such experiments and pub- 
lished his discoveries in his celebrated pamphlet An Inquiry into 
the Causes and effects of the Variolae Vaccinae. 
The inoculation with cowpox was called vaccination (vacca — 


cow). There was a storm of protest against this method of inocu- 
lation. Newspapers printed bitter attacks and said people would 
show the characters of cows if they had this filthy material from 
a cow introduced in them. The results, however, were so successful 
that vaccination was gradually accepted as the. only means of con- 
trolling smallpox, and the old method of inoculation was soon 
forbidden. Napoleon had all his soldiers who had never had 
smallpox vaccinated. The Empress of Russia urged its practice 
in Russia. Spain and Sicily also introduced vaccination. 

About 1800, at a meeting of the American Academy of Arts and 
Sciences, presided over by the President of the United States, 
John Adams, the introduction of vaccination into America was 
first considered. A supply of vaccine material was secured, and 
a Dr. Waterhouse vaccinated his five-year-old boy. He afterward 
vaccinated other members of his family. They became immune 
to smallpox infection. Later Thomas Jefferson became interested 
and he had the members of his family vaccinated. From that 
time on the practice of vaccination spread rapidly through the 
country. The vaccine virus tends to stimulate certain cells of 
the body to produce substances known as anti-bodies which re- 
main in the blood as a protection against disease. When a vac- 
cinated person is exposed to smallpox, he is already fortified by 
the anti-bodies which will act against the smallpox bacteria. 

Nature and symptoms of smallpox. Smallpox mortality is 30 
per cent greater among unvaccinated than among vaccinated 
persons. Children are particularly susceptible. In the Montreal 
epidemic of 1885-1886, 2717 of the 3164 deaths were children 
under ten years of age. 

Smallpox is caused by a filterable virus. About three days 
after becoming ill with smallpox, little abscesses or pustules 
form. If the pustules are deep, affecting the dermis seriously, 
pits or pock-marks will always show on the skin. The scales 
and crusts from the healing pustules are highly infectious, as are 

Number of Cases and Deaths from Smallpox in the United States 

1921 1923 1925 1927 

Cases Deaths Cases Deaths Cases Deaths Cases Deaths 

1. Alabama 

2. Arkansas 

3. Arizona 

4. California 

5. Colorado 

6. Connecticut 

7. Delaware 

8. District of Columbia 

9. Florida 

10. Georgia 

11. Idaho 

12. Illinois 

13. Indiana 

14. Iowa 

15. Kansas 

16. Kentucky 

17. Louisiana 

18. Maine 

19. Maryland 

20. Massachusetts 

21. Michigan 

22. Minnesota 

23. Mississippi 

24. Missouri 

25. Montana 

26. Nebraska 

27. Nevada 

28. New Hampshire 

29. New Jersey 

30. New Mexico 

31. New York 

32. North Carolina 

33. North Dakota 

34. Ohio 

35. Oklahoma 

36. Oregon 

37. Pennsylvania 

38. Rhode Island 

39. South Carolina 

40. South Dakota 

41. Tennessee 

42. Texas 

43. Utah 

44. Vermont 

45. Virginia 

46. Washington 

47. West Virginia 

48. Wisconsin 

49. Wyoming 

108,135 764 31,782 
* U. S. P. H. Reports. ** Reported by state, 
t Compiled by the American Association 























































































































































. . - 












































































































































































184 36,937 69932,102 138 
—-Information lacking, 
for Medical Progress. 



the contents of the pustules. If the disease is severe, the eyes, 
ears, and kidneys may be irreparably damaged. Recovery from 
one attack of smallpox usually leaves the individual immune ±o 
all subsequent attacks. 

Spread. Smallpox is very communicable, that is, it is readily 
spread by contact. The smallpox virus may enter the body 
through the respiratory system, or through the digestive system. 
It is carried by discharges from the mouth and nose, or by the 
pus and scabs, which may get in food, or on articles used by 

Prevention of smallpox. Because of the extremely communi- 
cable nature of smallpox, isolation or quarantine of all patients 
is essential. Sanitary precautions of all kinds should be taken 
in handling the patients and all the articles used by them. Ex- 

1 924- -V 


















Two groups of states have been compared. The chart on the left indicates those states having 
compulsory vaccination; the one on the right indicates local enforcement of the law. 

tensive education and widespread publicity as to the value of 
enforcing vaccination are necessary in order to keep the disease in 

WH. FITZ. AD. BIO. — 28 . 


check. A vaccination against smallpox lasts from five to seven 
years. After that time there should be a second vaccination. 
The second vaccination may produce immunity for life. By im- 
munity is meant the ability to resist disease. All children should 
be vaccinated before they are nine months old. Vaccination 
during epidemic periods is also wise. 

The vaccine for smallpox is prepared by first developing the 
causative organisms in the body of young female calves. After 
determining that the calves are perfectly healthy, they are 
thoroughly cleaned and inoculated with the crusts collected 
from the vaccinations of healthy children. Cysts or vesicles are 
formed in about five or six days and the contents of these vesicles 
are scraped off and ground into dilute glycerine in order to des- 
troy all harmful bacteria. This product is then tested several 
times, in many ways, for purity as well as for effectiveness. The 
material is then put up in small tubes ready for use. 

Value of vaccination. The gradual disappearance of smallpox 
is due largely to the widespread use of vaccination. In coun- 
tries where vaccination is not required, smallpox is still causing 
the deaths of thousands of people each year. It is still one of 
the main causes of death in China and India. Between the 
years 1918 and 1922, India reported 63,553 deaths from this 
disease alone. In Russia, between the years 1902 and 1914, over 
a million persons became affected with smallpox and over half 
a million died of it. 

In the Philippine Islands, prior to the occupation by the Amer- 
ican Army, it was estimated that more than 40,000 smallpox 
deaths occurred annually. Vaccination was introduced by the 
Americans in 1905, and has been continued ever since. There were, 
in 1903, 18,989 smallpox deaths, but this number has decreased 
rapidly until in 1916 only 239 deaths occurred from this disease. 
Then the effects of the first vaccinations wore off and people be- 
came careless about being revaccinated. This neglect resulted in a 


serious epidemic in 1918. During this year, 60,447 deaths oc- 
curred. At this time, only one case developed among the 5422 
vaccinated United States troops who were stationed on the Islands. 

There are still about 70,000 cases of smallpox in the United 
States annually, because vaccination is not universally enforced. 
In two states where vaccination is not required, there are many 
cases of smallpox. In one of these states there were over 2000 
cases and 230 deaths reported in 1926 ; in the other, 2413 cases 
and 31 deaths were reported in 1926. Contrasted with these 
states, a state where vaccination is rigidly enforced had, in the 
same year, only 56 cases and no deaths. 

Objections to vaccination not valid. When there is a specific 
prevention for a disease, as there is in vaccination against smallpox, 
it seems unbelievable that there are so many cases each year. 
The objections raised to vaccination are not well founded. One 
of them is that it causes lockjaw. There is no evidence to sup- 
port this belief. Since there is a scratch made in the vaccination 
process, there is probably the same danger of getting lockjaw as 
there would be from any scratch. There is no danger of lockjaw 
peculiar to the vaccination process. Strict government inspec- 
tion of the virus used in vaccination precludes the possibility of 
contamination. Ordinary precautions of a vaccination must be 
taken, however, to prevent infection. Some people think the 
vaccine is taken from a person who has smallpox and that this 
material may contain germs of the disease. The material is taken 
from calves and not people. The calves are examined carefully 
so as to eliminate the possibility of any disease being transmitted 
to people through the vaccine. The vaccine virus is always very 
carefully purified before being used. 

Questions and Suggestions 

1. Trace the early history of smallpox, including its introduction 
into America. 

2. Trace the history of inoculation to the time of Edward Jenner. 



3. Discuss the investigation and acceptance of vaccination for the 
prevention of smallpox. 

4. Give a report on the life and works of Edward Jenner. 

5. Discuss the nature of smallpox. How is smallpox spread ? - 

6. What are the chief preventive measures against smallpox ? 

7. Discuss some of the methods of inoculation used in the past. 

8. Has smallpox been checked to the fullest possible extent ? Give 
several reasons for" your answer. 

Supplementary Readings 

Broadhurst, Jean, How We Resist Disease (J. B. Lippincott Co.). 
De Kruif, P. H., Microbe Hunters (Harcourt, Brace & Co.). 
Haggard, H. W., The Science of Health and Disease (Harper & Bros.). 
Pamphlets published by the Metropolitan Life Insurance Co., New York 

Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.). 



Keystone View Co. 
Jupille battling with a mad dog. 

Keystone View Co. 
Interior of Pasteur Institute, 

How did Louis Pasteur control rabies ? Why does rabies still ex- 
ist? What advice did Louis Pasteur give to medical students? 

History of rabies. Rabies or hydrophobia is a very ancient 
disease. People termed it hydrophobia because a person bitten 
by a mad dog develops a fever and a thirst ; yet the attempt to 
drink water produces such painful convulsions that he develops a 
dread of water. Aristotle thought that man was not subject to 
rabies. Pliny the Elder recommended the livers of mad dogs as 
a cure. Galen advised a compound of crayfish eyes. Sea bathing 
was thought to exert a curative power. In 1780, in France, a 
prize was offered to the person who could give the best method for 
treating rabies. It was won by a surgeon-major who recom- 
mended cauterization or the burning of the infected area with red- 
hot irons. 

Rabies was one of the dread diseases of the past. People were 
so terrified of victims that had been bitten by mad dogs or wolves 
that they frequently strangled or suffocated them. They were 
afraid of contagion in nursing a case of rabies, since all knew that 
rabies meant certain death. A law was passed in France in 1810 
prohibiting the murdering of people suffering from rabies. 



Pasteur (1822-1895). About 1882, Louis Pasteur/ a French 
scientist, realizing that Jenner and others had successfully immu- 
nized persons by vaccination, decided to ar>pl^ the*- same principle 
to rabies. He had learned several things about the disease : 
(1) that the virus of rabies was contained in the saliva of mad 
animals; (2) that it was communicated through bites, and that 
the period of incubation varied from a few days to several 
months. He thought that there must be some way of prevent- 
ing the development of the disease during this long period of 

Pasteur had examined certain microorganisms in the saliva of a 
child that had died of rabies. He thought these were the causative 
organisms. When he injected them in animals, however, they 
failed to produce rabies. Pasteur inoculated rabbits "with saliva 
from rabid dogs. Hydrophobia took months to develop and some- 
times did not develop at all. Then he introduced blood from 
rabid dogs into rabbits and again was unsuccessful. Pasteur sus- 
pected the disease was in the nervous system and believed that 
explained the long period of incubation. He took particles of the 
brain of an animal that had died of hydrophobia and injected them 
into a number of animals. They all developed and died of hydro- 
phobia. Evidently, the particles of the brain were more potent 
or virulent than the saliva in causing rabies. Pasteur was unable 
to use his usual method of investigating disease. He could not 
isolate the germ and cultivate it in an artificial medium, because 
he could not detect the germ. 

Next, he suspended in a sterilized vial a fragment of the brain 
of a rabbit that had died of hydrophobia. As the fragment grad- 
ually became dry, its virulence or strength decreased until, at the 
end of fourteen days, it proved to be harmless when crushed, mixed 
with pure water, and injected under the skin of some dogs. The 
next day the dogs were inoculated with brain which had dried for 
thirteen days. The inoculations were continued, using fragments 



of brain of increasing virulence until the brain of a rabbit thaf had 
died the same day was used. It was found that the treated dogs 
were immune from hydrophobia. 

Pasteur invited a commission of 
scientists to investigate his work. 
Rabid dogs were permitted to bite 
healthy dogs that had been treated 
with Pasteur's inoculations and 
some that had not been treated. 
The former did not contract 
rabies, the latter did. The scien- 
tists were enthusiastic over this 
scientific triumph. Pasteur then 
showed that the development 
of rabies in dogs that had been 
bitten by a rabid dog could be 
prevented by means of similar 

In 1885, a little Alsatian boy, 
Joseph Meister, was brought by 
his mother into Pasteur's labora- 
tory. He had been horribly bitten 
by a mad dog. Pasteur, after con- 
sultation with other scientists, 
decided to give him inoculations 
of brain and spinal cord material 
that he had prepared. His first 
inoculation was material that had 
dried fourteen days. This was fol- 
lowed by further inoculations, of 
increasing strengths. The treatment lasted ten days and included 
twelve inoculations. It was successful in preventing rabies and was 
the first successful treatment for rabies given to a human being. 

Pacific & Atlantic Photos 
The people of Chicago have erected a 
monument in recognition of the inesti- 
mable service of Louis Pasteur to human- 
ity. Millions of people passing the monu- 
ment give occasional thought to the 
nobility of character and devoted life of 
the great scientist. 



Foreign scientists flocked to Paris to learn more about the treat- 
ment. Letters came from all over the world for information. 
Children were brought from far and near for treatment. From 
America, four small children, who had been bitten by mad dogs, 
were sent over to Pasteur for treatment. A public subscrip- 
tion was conducted by a New York newspaper in order to supply 
the funds for their treatments. The inoculations given these chil- 
dren by Pasteur were successful. Nineteen Russians who had been 
bitten by a mad wolf were brought to Paris by a Russian doctor. 
The only French word they knew was " Pasteur." Two weeks had 
elapsed between the time they received their wounds and their 

arrival in Paris. Although 
they were horribly bitten, 
all but three of them were 

Pasteur was one of the 
first scientists to develop a 
method of weakening or at- 
tenuating organisms by lab- 
oratory procedures for use 
as a vaccine. To-day, all 
our large cities have Pasteur 
Institutes, or similar divi- 
sions of the Health Depart- 
ment for giving treatment 
for rabies. 

The nature of rabies. 
Rabies is an infectious dis- 
ease of dogs, wolves, cats, 
and sometimes of horses, 
cows, rabbits, and other ani- 
It may be communicated to human beings. The infection 



Vaccines for the treatment of hydrophobia are 
prepared from the spinal cords of animals that have 
died from the disease. The cords are suspended 
in a bottle which has a water-absorbing material 
in the bottom of it. As the cords dry, they become 
attenuated or weakened in virulence. 


is from an organism not yet cultivated or positively identified. 


It is a filterable virus which attacks the central nervous system. 
This virus can be found in the salivary glands and in the saliva of 
infected animals. . 

If some of the nervous tissue of an animal that has died from 
the disease or been killed during the course of the disease be ex- 
amined microscopically, characteristic spherical inclusions will be 
found. These structures are called Negri bodies and the appear- 
ance of them in the brain cells is the principal method of determin- 
ing whether or not a suspected animal is rabid. If they are found 
in the brain of an animal which has bitten a human being, the 
Pasteur treatment is immediately prescribed for the person or 
animal bitten. The relation of these Negri bodies to the causa- 
tive organism is not yet known. To confirm the diagnosis, a bit 
of the brain of the dead animal is sometimes injected into an- 
other animal. If the disease is rabies, the second animal will 
become sick and die. Because the rabies organism attacks the 
central nervous system, the muscles controlled by that system 
are secondarily affected and, consequently, paralysis is a charac- 
teristic of the disease. 

The effect of rabies on animals. When a dog becomes sick 
with rabies, only an expert would suspect what the trouble is. 
Many cases do not show violent symptoms, although most cases 
begin with a characteristic change in the animal's disposition. In 
general, the course of the disease is marked by a change in dis- 
position, irritability and excitement, which is usually followed 
by depression, paralysis, and death. 

Transmission. Rabies is transmitted to man by the bite of an 
infected animal, because the germs or virus of the disease are in 
the saliva. The bite breaks the skin and introduces the causative 
organism. There have been cases in which persons contracted 
the malady from being scratched by the animals or from allowing 
the dogs to lick a hand upon which some scratch or wound 


Cure. There is no known cure for rabies once it definitely de- 
velops. The only possible help a patient may secure is the pre- 
ventive treatment which should be given early. 

Prevention. One should always be careful in handling sick 
animals, especially dogs and cats. If a dog, suspected of having 
rabies, is running loose, it should be penned up for ten days, and 
if it does not develop rabies in that time it is safe to let it out. 

Most departments of health examine and keep under observa- 
tion all dogs suspected of having rabies. They will also take care 
of dogs that have been bitten by other animals which are suspected 
of having the disease. In order to prevent rabies, the health 
departments of many states require that all dogs be muzzled. 

To prevent the development of rabies in a person bitten by a 
rabid animal, the wound must be washed at once. Under the 
care of a competent physician, it should be treated with a strong 
antiseptic or be cauterized. Then the preventive vaccination 
treatment must be begun at once. This builds up the person's 
resistance to rabies. Practically no one has ever been harmed by 
this treatment. In all cases, it is of utmost importance to give 
the Pasteur treatment immediately. 

Large deep bite-wounds are the most dangerous, especially those 
about the face, head, back, or any part where nerves and lymphatics 
are abundant. A bite through clothing is usually less dangerous 
than one on the bare surface. 

The eradication of rabies in man depends upon its prevention 
in domesticated animals. This problem of prevention still exists 
in certain sections of the world, as the disease is very prevalent 
among wild animals which transmit it to dogs and other domes- 
ticated animals. In 1923, approximately 22,000 persons in the 
United States applied for and received the Pasteur treatment. 

In England, the enforcement of the law requiring the muzzling 
of dogs and a quarantine on all animals imported from other 
countries eliminated the disease entirely from 1903 to 1918. 



It is now possible to give prophylactic or preventive treatment 
to dogs, which render them immune to rabies. In 1924, approxi- 
mately one hundred thousand dogs in 
Japan were immunized, and the num- 
ber of cases of the disease was reduced 
to forty-one. Before that time there 
were approximately 1700 cases of rabies 
each year among the dogs. 

Pasteur's ideals. In closing a chap- 
ter that brings in a part of the work 
of a remarkable man, no more fitting 
tribute can be paid him than to repeat 
a part of a speech made to Pasteur on 
his seventieth birthday. The great 
theater of the Sorbonne was filled by 
committees from Denmark, Sweden, 
and Norway. The members of the 
French Institute and the Professors of 
the Faculties were there. Students of 

medicine had crowded into every available place. Lister was 
there, representing the Royal Societies of London and Edinburgh. 
Many offerings were tendered Pasteur, many tributes paid, and 
the last was made by the President of the Students' Association, 
who said, " You have been very great and very good ; you have 
given a beautiful example to students." 

Pasteur's voice, weakened by his emotion, could not have been 
heard over the large theater. His reply was read by his son : 

"... do not let yourselves become tainted by a deprecating 
and barren skepticism, do not let yourselves be discouraged by 
the sadness of certain hours which pass over nations. Live in the 
serene peace of laboratories and libraries. Say to yourselves first : 
' What have I done for iny instruction ? ' and, as you gradually 
advance, ' What have I done for my country ? ' until the time 

A sketch of a brain smear prep- 
aration of a suspected " mad " dog. 
The presence of nucleated Negri 
bodies led to a diagnosis — "rabid 
animal." The boy bitten by this 
animal was given the Pasteur treat- 
ment and did not develop hydro- 


comes when you may have the immense happiness of thinking 
that you have contributed in some way to the progress and good 
of humanity. ..." 

Questions and Suggestions 

1. State some of the ancient ideas on the treatment of rabies. 

2. Describe Pasteur's experiments with saliva and blood. 

3. Discuss Pasteur's experiments with dried brain and spinal cords. 

4. Discuss the first vaccination of animals against rabies. 

5. Discuss the first vaccination of a person against rabies. 

6. What effect did the discovery of vaccination against rabies have 
on the world ? 

7. What stimulus did Pasteur give later scientists by his work on 
vaccination ? 

8. Discuss the cause, method of invasion, and symptoms of rabies. 

9. Discuss methods of preventing and controlling rabies. 

10. What is the importance of vaccination against rabies ? 

11. Is there anything in Pasteur's speech that indicates why he has 
been called one of the finest scientists the world has ever produced ? 

12. Give a report on the life and work of Pasteur. 

Supplementary Readings 

Broadhurst, Jean, How We Resist Disease (J. B. Lippincott & Co.). 
De Kruif, P. H., The Microbe Hunters (Harcourt, Brace & Co.). 
Haggard, H. W., The Science of Health and Disease (Harper and Bros.). 
Vallery-Radot, Rene, The Life of Pasteur (Doubleday, Page, and Co.). 





Robert Koch. 

Edward Livingston Trudeau. 

How was the germ of tuberculosis discovered? Was the discovery of 
the tuberculosis germ due to careful scientific investigation ? Is tuber- 
culosis a curable disease? 

Pasteur presented his germ theory of disease to the world in 
1860. At that time many people did not have much faith in his 
work, but he cleared the way for much of the work done by other 
scientists of his own day and later. The investigation of tuber- 
culosis would probably have been impossible had it not been for 
Pasteur's work. 

Dr. J. A. Villemin. In the nineteenth century, medicine was not 
based on scientific research. Pasteur's work on microorganisms 
was not accepted generally until the latter part of the century. 
In 1864, Dr. J. A. Villemin, one of the few real scientists, by means 
of experimental research, brought out the idea that tuberculosis 
was a disease which reproduced itself and could be reproduced 
only by itself. In brief , he said it was caused by a specific organism, 
and could be communicated from one person to another. In 
order to demonstrate the fact that tuberculosis was communi- 
cable, he experimented on animals. He took some sputum of a 
tubercular patient, spread it on cotton wool which he dried and 
made into a bed for guinea pigs. The pigs, in time, became tuber- 



cular. People did not accept Villemin's findings. They still clung 
to the idea of spontaneous generation of this and other diseases. 
In fact, he was treated as a disturber of medical order and beliefs. 

Professor J. Cohnheim, 1839-1884, at Breslau, found that he 
could give tuberculosis to rabbits by putting a bit of the tubercular 
patient's diseased lung into the front chamber of a rabbit's eye. 
Here he could watch the little island of tissue spread and do its 
deadly work of building tubercles. 

Koch discovers the cause of tuberculosis. Robert Koch (1843- 
1910) built on Cohnheim's work. As long as animals could be 
inoculated with the disease, he could experiment with them. 
At this time, probably, one out of every seven people was dying 
of tuberculosis. Koch took tubercles from a man who had died 
of tuberculosis and injected them into the eyes of guinea pigs and 
rabbits. While he was waiting for them to develop signs of the 
disease, he examined tissues of people who had died of tuberculosis. 
No microorganisms showed. He stained the tissues with different 
dyes, in order to see the germs. (As he worked, he kept dipping 
his hands into bichloride of mercury, for Lister, the English sur- 
geon, had demonstrated the importance of antiseptics in checking 
infections.) Finally, Koch smeared some material from tubercles 
of a tubercular person on a glass slide, dipped it in' a certain dye, 
and mounted it under his microscope. He saw slender rod-shaped 
organisms very minute in size, about 1 5 I of an inch long. 
The last stain had been successful. 

In the meantime, the guinea pigs and rabbits, which he had in- 
oculated became sick and died. He examined their bodies, and 
found tubercles which he stained and examined microscopically. 
In every case he found the always slender, curved rods. He ex- 
amined the bodies of many people who had died of tuberculosis 
and always found tubercles. * Then he injected (inoculated) tuber- 
cles into guinea pigs, rabbits, dogs, cats, and many other animals. 
Invariably all the animals inoculated with the tubercles died of 


tuberculosis. As each animal died, Koch examined its tissues and 
always found tubercles and the slender rods. Then he examined 
tissue after tissue of healthy animals and found no tubercles. _ 

He was not yet positive that he had discovered the tubercle 
bacilli. He decided that he must first cultivate them outside the 
body of animals and then introduce the cultivated organisms into 
healthy animals. If the inoculated animals became tubercular, it 
would indicate the presence of the organisms. He made every 
kind of broth then known for the cultivation of germs. He kept 
some of his tubes and bottles* at the temperature of the room, 
some at the temperature of a man's body, and others at fever 
temperature. He infected his broths with portions of the in- 
fected lungs of guinea pigs. No tubercular organism grew in 
any of the broths, regardless of surrounding temperatures. 

Undaunted, he thought he would try tissue extracts for his 
media. Possibly tissues had peculiar materials that were essential 
for the growth of the tubercle bacillus. He obtained serum from 
blood, mixed it with agar, heated it to make it set, and placed it 
on slants in test tubes in order to get long, flat surfaces on 
which to grow the bacilli. He streaked the serum-agar with a bit 
of the infected lung of a guinea pig that 
had just died of tuberculosis. Then he 
placed his tubes in an incubator at the 
same temperature as that of the guinea 
pig's body. On the fifteenth day the 
serum jelly was covered with tiny glisten- 
ing specks. When magnified with a hand 
lens, they appeared as dry, tiny scales. <g^— Jn^SSi 
He stained and mounted one of the scales The rod-shaped structures, 
under the microscope and found the same are'toe bacuit thatVusTtu- 
bacillus which he had discovered in the lung t> erculosls - 
of tubercular victims.^ He had grown tubercle bacilli outside the 
body of an organism. He then inoculated animals with the bacilli 


grown on his serum-agar; the inoculated animals contracted 
tuberculosis and died. 

He decided to try one more experiment. He wondered how 
people contracted tuberculosis, and thought that they had prob- 
ably inhaled some of the dust particles of which Pasteur had 
spoken, or possibly were infected by droplets which tubercular 
people scattered in the air when they coughed. He sprayed 
bacilli into the air breathed by certain animals. The animals 
became tubercular and died. 

The method of investigating an unknown disease that Koch 
used in 1882, is still being used to-day. His method is commonly 
known as Koch's postulates which are : (1) isolate the probable 
germ from the diseased organism ; (2) grow the germs in an arti- 
ficial media; (3) transfer the germs from the culture to an 
organism and notice whether they will produce the disease; 
(4) obtain some of the germs from the second organism and iden- 
tify them. From Koch's investigation, dates the beginning of the 
triumph of bacteriology. 

Koch reported his findings before the Physiological Society, in 
Berlin, in March, 1882. The most brilliant men of science in 
Germany were there. There was no word of criticism against 
his work ; it was too thorough and convincing. The news of his 
discovery spread rapidly, and the entire world soon learned of his 
work and his methods of investigating diseases. 

Edward Livingston Trudeau. While Koch was investigating 
the cause of tuberculosis, there was a man named Trudeau living 
in the United States. , He was taking care of a tubercular brother 
whom he bathed, fed, and even slept with. His doctor warned 
him not to open the windows as it was bad for the brother's cough. 
The brother finally died. 

Trudeau then studied medicine, became a doctor, but did not 
practice long, before he realized that he had tuberculosis. Like 
all people of his day, he thought tuberculosis meant certain death. 


When he realized that he had tuberculosis, he went to end his 
days in the Adirondack Mountains which he loved. Strangely 
enough, his health be- 
gan to improve. Two 
or three doctors, hear- 
ing of his improvement, 
sent other tubercular 
patients to him and a 
small sanitarium was 
thus started in the 
northern part of New 
York State. Trudeau 
heard of Koch's work 
and went back to New 
York city to learn the 
laboratory methods of 
isolating the tubercle 
germs. Then, return- 
ing to the mountains, 
he started experiment- 
ing on rabbits. He 
took three sets of rab- 
bits. He inoculated two 
of them with tubercle 
bacilli. One of these 
sets he placed in a dark 
camp box that was 
poorly ventilated, and 
gave them an insuffi- 
cient diet. The other that had been inoculated he let roam on 
an island in the Adirondacks where there was plenty of air, sun- 
light, and food. The third set, that had not been inoculated, 
was also put in very unfavorable surroundings. The results were 

WH. FITZ. AD. BIO. — 29 


Prospective deathrates, l$)2d to 1937 

Original Registration States and District of Columbia 

PER 100,000 PER IOO.OOO 




- 160 

- 160 

■ 140 

■ 120 

- too 


' 40 


















. UJ.I. 

1 1 1 1 

I I 1 I 





30 1905 1910 1915 1920 1925 I5J0 1955 



If the trends between 1900 and 1922 are averaged, the 
expectation of the tuberculosis death rate for 1937 is about 
40 per 100,000. If the decrease of 1926 and 1927 con- 
tinues, the death rate in 1937 would be 20 per 100,000. 
A greater decrease than has yet been shown is necessary 
to bring the death rate to 0. (From Health and Wealth by 
Dublin, Harper & Bros.) 


that the rabbits living in the good environment recovered from 
the effects of the inoculation. The inoculated rabbits living in 
poor conditions died within three months from tuberculosis. The 
rabbits that had not been inoculated but were in the poor envi- 
ronment did not show tuberculosis, although they were not in 
good physical condition. Repeating similar experiments, he proved 
that unsanitary conditions, alone, will not cause tuberculosis ; the 
germs must be there. He also showed that unfavorable envi- 
ronments favor the development of tuberculosis and good living 
conditions help to check the disease. 

Trudeau, with the help of another doctor, started his sanita- 
rium at Saranac Lake. He built a number of small cottages and 
thus started the Cottage Plan of Tuberculosis Sanitariums. He 
enforced a routine which included plenty of fresh air, rest, good 
food, and sunlight. This method was revolutionary. Trudeau 
was the first physician in the United States to teach the impor- 
tance of fresh air in the treatment of tuberculosis. Since his 
time numerous sanitariums have been built over the entire world. 

Causative organism. A rod-shaped bacillus is the cause of 
tuberculosis. There are many types of these bacilli. They 
attack practically all warm-blooded animals. Most of the tuber- 
culosis among children under five years of age is of the bovine 
type. It is the type that attacks cattle and usually is taken in 
by the child with milk. 

The bacilli of tuberculosis may attack any part of the body but 
once present the germs are very likely to eventually attack the 
lungs. They actually feed on and destroy lung tissue. They 
form little nodules or tubercles filled with a cheesy material and 
produce poisons or toxins. There is always a toxin called an en- 
dotoxin produced within the bacillus and probably an exotoxin, 
an excretion, is given off. A slight tubercular infection almost 
always occurs in childhood. The normal resistance of the child's 
body overcomes the disease by either killing the bacilli or keeping 



them from growing. In the latter case the germs are still alive 
and will become active again, whenever the resistance is weakened 


Adjusted* Deathrates per IOQOOO. Tubercubsis-all forms. 1922 


State Pate 







> NEW YORK 930 







VERMONT 67 fl 




OHIO 61.6 

MAINE 61.2 






hats-* o » »o iso 200 m 100 













100 150 200 ISO WO 

* Pates adjusted for differences of sex and aie constitution of population. 

* * Includes States with populations containing number or proportion of colored 
persons insufficient to warrant separate tabulation. 

Make a graph from the latest figures of your own and neighboring states and compare it 
with this chart. Give the possible reasons for a high mortality among the colored population. 
(From Health and Wealth by Dublin, Harper & Bros.) 

by infection, malnutrition, overwork, and fatigue. Data concern- 
ing the prevalence of tuberculosis in childhood and the subsequent 
recovery of the children from it is known, because investigation 
proves that the lungs in practically every dead body examined 
and the X-rays of living lungs show old scar tissue. The scar tis- 
sue is characteristic of tuberculosis attacks. Bacilli that get into 
the blood are frequently carried to a lymph gland, where white 
corpuscles in great numbers attack and destroy them. The body, 
meanwhile, builds a hard wall of 'lime salts around the infected 
gland, so that the infection is thus removed from the circulation. 
Sometimes infected glands are cut out to prevent the spread of 
the germs. Tuberculosis is not hereditary, but susceptibility to 


the disease is probably inherited. People who know there is a 
history of tuberculosis in the family should be especially careful to 
live very hygienically. When this is done, they are not likely to 
contract the disease. Poor environment is a predisposing cause of 
tuberculosis. If a mother has contracted the disease, her child is 
likely to live in the same environment and will probably contract 
the disease. For the good of the child, it should be taken from its 
parents in such cases, so that it can build up a strong resistance. 

Symptoms of tuberculosis. The symptoms are several. Fever, 
especially in the afternoon, even in earlier stages before coughing 
has started, habitual coughing and spitting, poor appetite, faulty 
digestion, and steady loss of weight are usually indicative of an 

Diagnosis. Diagnosis consists of a microscopic examination of 
the sputum for the bacilli. A careful examination of the general 
physical condition including an X-ray examination of the lungs 
is made. The X-ray photograph will show any scar tissue. A 
tuberculin test is sometimes made. This is given by putting toxins, 
squeezed from tuberculosis germs, under the skin of the suspected 
patient. If the disease is present in the patient, there will be an 
increase in fever and pulse, an increase of inflammation of the 
affected part, and a redness at the- point of infection. A nega- 
tive test is conclusive proof of the absence of the disease. A 
positive test may indicate a past as well as a present infection. 
Since a positive reaction may be obtained from nearly every 
adult, the test is chiefly valuable, for young children. 

The tuberculin test for cattle has been used for years. Accord- 
ing to laws in some states, state inspectors test the dairy cows. 
When the test shows the presence of the disease, the cow is killed 
and the farmer is partially reimbursed for the loss. All states 
do not have this law. Some states have such laws, but let the 
townships decide whether or not they will be enforced. 

Spread of tuberculosis. Tuberculosis is spread in innumerable 



ways. Two modes of entrance of the germs into the body are 
through inhalation to the lungs and through ingestion to the ali- 
mentary tract, and thence to the lungs. The disease may^be 
actually spread from person to person by : (1) spray thrown out 
in coughing and sneezing, a droplet method of infection ; (2) con- 
taminated objects, such as drinking cups and pencils, handled or 
used by a tubercular person; (3) personal contact, such as kiss- 
ing and handshaking, with an infected person ; (4) food infected 
by being coughed on or handled by a tubercular person ; (5) dust 
from street or car, containing dried sputum of a tubercular 
patient ; (6) houseflies carrying tubercular germs on their bodies 
may crawl over and infect food ; (7) milk and butter of tuber- 


Percentage, Phthisis Deathrate in Specified Occupation 
of Deathrate among Farmers. England and Wales, 1910- 1912. 



Tin miners 


Cutlers, scissors makers 


File makers 








Lead miners 


Potters-earthenware mfr. 


Laborers (unspecified) 


$eamcn.etc(merchant service 

' 456.1 



Brass and bronze workers 






Hotel keepers, saloon keepers 


Vjkh and dockmafers. jewelars 




Glass manufacture 








* t » 10 I i 


Painters, decorators 
Copper workers, coppersmiths 
Kach inists. boiler-fnahers. milrwrighb 
Carpenters. Joiners 

Domestic coachmen, grooms 
Vfeol. worsted manufacture 
Cotton manufacture 
All storekeepers 
Coal miners 

Stationary engineers and firemen 
lron-miners,quarriers * 
Brick,plain Ue.terra-cotta makers 
ApVicultural laborers 

Motor car drivers 
Railway engine men 
Farmers, graziers, etc. 



Compile figures for your own country, state, or city and compare them with this table. 
(From Health and Wealth by Dublin, Harper & Bros.) 

cular cows. (The tuberculin test shows that 15 per cent of the 
cows of to-day are infected with tuberculosis.) 


Treatment. Since the body itself must fight this disease, it 
should be given the best possible environment under which to 
work. Giving the patient the most healthful conditions is the 
most we can do for him. Fresh air, sunlight, plenty of sleep, 
freedom from worry or work, and an abundance of easily digested 
food such as milk and eggs are the main factors in the treatment. 
Outdoor treatment is usually best if the climate is mild. It is best 
and most always necessary to have expert treatment at a sanita- 
rium under the supervision of a doctor, for at least six months. 

Prevention. . There are a number of measures to be observed 
by individuals in order to prevent infection : keep the resistance 
of the body high by proper living habits ; have a general physical 
examination once a year ; teach or compel all tubercular persons to 
cover their mouths with handkerchiefs when coughing ; use paper 
cups and paper towels in public places and use only sanitary 
drinking fountains ; keep the dust down, by using a vacuum 
cleaner and damp cloth in the home, and by sprinkling and flushing 
the streets ; keep flies out of the house by screening the doors and 
windows, and off the food by covering it ; report all cases of 
tuberculosis not under proper medical care to the Board of Health. 
The communities can also help to control the spread of tubercu- 
losis. They should require the inspection and pasteurization of 
all milk. Only raw milk from tuberculin-tested cows should be 
sold. They can also aid by enforcing the existing laws against 
spitting in public places ; requiring Board of Health certificates 
from the persons who handle foods ; providing for healthful living 
conditions in tenement houses ; and providing for more hospitals by 
fostering the sale of Christmas seals. Probably one of the most 
important ways of controlling the disease, is to educate the peo- 
ple against the dangers of tuberculosis and the best methods of 
preventing it. 

The tuberculin test was first devised by Koch in 1890. People 
kept insisting that he find a cure for the disease, since he already 



knew the cause of it. He was working on a tuberculin inoculation 
which could be introduced into people as a means of working up a 

International Newsreel 
Fresh air is invaluable in treating tuberculosis. Some sanitariums require patients to dress 
as lightly as possible, even in winter. The exposure of large areas of the body to air and 
sunlight is helpful in the treatment of tuberculosis. 

"resistance or an immunity. He was literally forced into publish- 
ing his work before he had tested it sufficiently. Doctors began 
to inoculate people with the tuberculin test devised by Koch. In 
many cases the results were fatal. Tuberculin inoculation then 
fell into disrepute. 

At present, a group of doctors is working on a tuberculin vac- 
cine at the Pasteur Institute in Paris. The vaccine consists of 


greatly weakened germ material. It is hoped that this will stim- 
ulate the body to make protective materials which will stay in the 
blood. If the vaccinated person then comes in contact with the 
active disease, he is already fortified and protected and should not 
contract the disease. In France, the average mortality among 
infants from tuberculosis is about 20 per cent. In a recent scien- 
tific experiment 969 infants who were born of tubercular mothers 
or were in direct contact with the disease were inoculated. 
Among the vaccinated infants, for the two years following vac- 
cination, the mortality for this disease was about one per cent; 
the mortality was nil after two years. The resistance lasted more 
than four years. Hence the infants were immunized or protected 
for the period when tubercular infection is most dangerous. 

Prevalence and economic importance. It is estimated that 
tuberculosis causes one tenth of all the deaths in civilized coun- 
tries ; until recent years it was the principal cause of all deaths. 
There are one million, five hundred thousand cases of active 
tuberculosis in the United States ; one hundred and fifty thousand 
deaths occur every year. The mortality, therefore, is approxi- 
mately ten per cent. There are probably twice as many deaths 
every year from the tubercle bacilli as there were among our 
military forces during the World War. 

The disease is estimated to cost the United States $225,000,000 
a year. The mortality was reduced from 224 for every 100,000 
people in 1911 to 114.2 in 1922, a reduction of 49.2 per cent. In 
1928 the deaths from tuberculosis were the lowest on record. 

Questions and Suggestions 

1. What was the contribution of Dr. Villemin to the investigation 
of tuberculosis ? 

2. Discuss the experiments of Koch. 

3. Name Koch's postulates. 

4. Look up and give a report on the life and work of Koch. 


5. What was Trudeau's contribution to the investigation of tuber- 
culosis ? 

6. Give a report on the life of Edward Livingston Trudeau. 

7. Discuss the cause, method of entering the body, part of organ- 
ism attacked, and effect on the body of the tubercle bacilli. 

8. Discuss the diagnosis of tuberculosis in people and in cattle. 

9. Name all the ways by which tuberculosis may be spread. 

10. What is the treatment for tuberculosis ? 

11. What precautions should be observed in order to eradicate 

12. What is the status of tuberculin vaccinations at present? 

13. Is tuberculosis increasing or decreasing? Is it sufficiently 
under control ? 

Supplementary Readings 

Broadhurst, J., How We Resist Disease (J. B. Lippincott & Co.). 
De Kruif, P., Microbe Hunters (Harcourt, Brace & Co.). 
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.). 
Haggard, H. W., The Science of Health and Disease (Harper & Bros.). 
Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.). 





Tetanus bacilli. 

Diphtheria bacilli. 

Can diphtheria be completely eradicated"? Is there any protection 
against scarlet fever ? What is the relation of tetanus to wounds? 

Three diseases that are somewhat similar in their methods of 
attacking the body are diphtheria, scarlet fever, and tetanus. 

History of diphtheria. Fairly accurate descriptions of diph- 
theria have been given by certain ancient Greeks. There is evi- 
dence that the disease has been known for many centuries. In 
1826, a scientist in France was the first to look upon diphtheria as 
a specific and infectious disease that was frequently spread by 
the use of a common drinking cup. He said that croup was a 
type of diphtheria, and he differentiated the disease from the 
sore throat of scarlet fever. 

Isolation of organism. Klebs, in Germany, in 1883, discovered 
bacilli, striped with bars or bands, in the throat of children sick 
with diphtheria. In 1884, some banded bacilli were isolated and 
stained with methylene blue by Emil Loeffler, who thought that 
they could not be the causative organisms of diphtheria. He 
was confused by the fact that some perfectly well children had 
these bacilli in their throats and some children who were ill with 
what seemed to be diphtheria did not have the germs. Loeffler 
grew the banded bacilli on broth and injected them under the 
skin of guinea pigs. The pigs died, although the bacilli did not 
spread, but stayed at the point of entrance below the skin. 



Isolation of toxin. In 1888, Roux and Yersin showed that the 
diphtheria bacillus produces a toxin. Roux had realized that 
the germs might secrete a deadly toxin which he attempted -to 
separate from the germs. He grew the bacilli on broth and used 
a porcelain filter that held back the germs, but permitted the 
soluble material to pass through. The filtered liquid was then 
inoculated into guinea pigs which developed the symptoms of 
diphtheria. Thus Roux showed that the diphtheria bacilli kill 
through a toxin rather than by the spread of the germs. Earl'er 
investigators of this disease were unsuccessful because they did 
not realize that the germs stayed in the throat and sent out 
toxins (exotoxins) which affected the body. The healthy people 
who had diphtheria germs were probably diphtheria carriers and 
the sick people who did not have the bacilli in their throats 
probably did not have diphtheria. 

The discovery of antitoxin. The toxic effects of the diphtheria 
bacillus led Von Behring to believe that blood contained certain 
chemical substances which would kill invading microbes without 
injuring the person or animal. After a series of experiments, 
he finally inoculated diphtheria toxins under the skin of guinea 
pigs that had recovered from diphtheria. 
They were not affected by the toxins, but 
when he inoculated toxins under the skin 
of guinea pigs that had not had diph- 
theria, they became ill. 

Von Behring obtained blood from guinea 
pigs that had recovered from diphtheria, 
separated the serum, and mixed it with Bacterium cUphtheriae 
diphtheria toxin. He injected this mix- The beaded appearance, 
ture of serum and toxin into healthy ^^^^ 
guinea pigs and they were not injured by carefull y p^pared culture, 
it. But, when he mixed blood serum from guinea pigs that had 
never had diphtheria with diphtheria toxin, and inoculated the 


mixture into healthy guinea pigs, they died. From these experi- 
ments, he concluded that guinea pigs which had contracted and 
recovered from diphtheria had something in the serum that safe- 
guarded them from subsequent attacks of the disease. He called 
this protective material antitoxin. His experiments showed that 
the guinea pig's body made protective antitoxins to combat the 
toxins of bacilli. These antitoxins remained in the blood of 
animals that recovered from diphtheria. 

He then decided to prepare an immune serum which would 
protect babies. He injected small amounts of diphtheria toxins 
into sheep and continued to give them doses of increasing strength. 
Ultimately, the sheep were immune to the most powerful diph- 
theria bacilli. Then he injected serum from the immune sheep 
into guinea pigs and later he inoculated diphtheria bacilli into 
these pigs. They were not affected by the bacilli. Evidently, 
the antitoxins made by the sheep's body were effective in pro- 
tecting the guinea pigs against diphtheria bacilli. One serious 
difficulty was that this immunity did not last. In 1891, Von 
Behring discussed the use of serum on babies, and in 1893 it 
was first used in the Children's Hospital in Berlin with some 
degree of success. 

The discovery of active immunity. The fact that sheep, goats, 
and horses used in the production of antitoxin seemed to develop 
a permanent immunity to the diphtheria toxin gave the basis for 
the next step in this work. Persons who had once been sick with 
diphtheria seemed to be free from further attacks. This gave 
support to the idea that the presence of toxins stimulates the 
human body to produce its own antitoxins. The action of the 
body in producing its own protective material is known as active 
immunization, and the resulting condition is active immunity. 

Investigators mixed antitoxin with toxin and found that the 
toxin was rendered harmless. Von Behring was the first to 
attempt to give a permanent immunity to children by means of 



this mixture, but his work was interrupted by the World War. 
Later, Dr. William H. Park of the New York City Laboratories, 
inoculated children with the antitoxin and toxin, known as toxin- 
antitoxin, and was successful in having them develop an active 
immunity which was permanent. 

A test for immunity. In 1913, Dr. Bela Schick devised the 
Schick test of susceptibility. When small quantities of toxin are 
put under the skin of children, the reaction will indicate whether 
the child is naturally immune or not. If naturally immune, the 
toxin will be neutralized by antitoxins in the blood and no effect 
is produced. If not immune, a slight local irritation results in 
the form of a red spot which appears and disappears within a def- 
inite time period. It indicates that there are not sufficient anti- 
toxins in the blood to neutralize the small amount of toxin injected. 

Cause of diphtheria. Diphtheria (sometimes called " mem- 
branous croup ") is justly regarded as one of the most dreaded of 
the diseases of childhood. It is a disease of temperate climates, 
occurring most frequently in the colder months. In cities, the 
disease is always more or less prevalent ; in rural communities, it 
is more likely to occur in 

Deaths from diphtheria 
occur chiefly among chil- 
dren less than five years 
old. There is a definite 
increase in susceptibility 
to the disease during the 
first two years of life, 
and a gradual develop- 
ment of immunity there- 
after, especially if the 
individual lives in a well- 
populated district and is more or less exposed to the disease. 


•un&ef 3 •morvtKs 
3to6 'mont'hs 

6 tooths to ly**. 

1 -*© ayewv 

2 -fe 3 ye<xr*s 

3 4o 3 VGcers 

lO*© 2oVea/r& 

over aoVeart 


36 1 








Am. Ass. for Med. Prog. 
Note that the ages of greatest susceptibility to diph- 
theria is among the pre-school children group. This 
is where the greatest prevention work should be done. 



DlPWf HEPIA. Tnust g> 
f romTfesf ybrfc State 

Diphtheria is caused by the growth of the diphtheria bacillus, 
usually in the throat, nose, or larynx. This germ is a slender, 
slightly curved, club-shaped rod, which does not form spores, 
and which, when stained, shows characteristic staining particles. 
These particles make the stained organism easily recognized. 

Effect on the body. The diphtheria bacilli grow in the affected 
part (throat or trachea usually) and first cause inflammation and 
swelling, and later form a grayish membrane. The bacilli multiply 
in the membrane and at the same time throw off virulent toxins 
which will cause death when absorbed by the body in sufficient 
quantities. If the membrane grows down sufficiently into the 
trachea, death may occur from suffocation. The action of the 
toxin on the heart is particularly severe and sometimes brings about 
heart defects, even after the patient has become convalescent. 

How diphtheria is 
carried. Each new 
case of diphtheria is 
derived from a previ- 
ous case of diphtheria 
or from a diphtheria 
carrier. The disease 
may be spread from 
infected to well per- 
sons by direct contact, 
as by kissing or by 
mouth spray given off 
in sneezing or cough- 
ing. The germ-laden 
droplets of such mouth 
sprays may enter the 
mouths of others or 
be breathed in with" the air, or they may be carried to the mouth 
from the hands in eating. Indirectly, the bacilli may be trans- 

laas •89 , 9TOT9S'97 '900 'MWoB KiT*V> , l& SO 22 '24 '26 "IS, '3Q 

Diphtheria is a disease that can be completely controlled 
through scientific measures. It has been estimated that 
the cost of treating one case of diphtheria will protect two 
hundred children from the disease. Note the effect of anti- 
toxin and toxin-antitoxin on the death rate in New York 



compare your- 
town cDithL' 

cases AUBVRN.XX 

<mly one 
«*^« aeathfrom. 


1324 to 1^29 

19*2 19% 

mitted through the agency of various objects such as pencils, 
apples, candy, eating utensils, drinking cups, or the like, which 
have been handled or used 
by infected persons. Diph- 
theria carriers are seem- 
ingly well individuals who 
harbor the bacilli in their 
bodies. Persons who have 
been in contact with those 
suffering from diphtheria 
are especially likely to be 
carriers, yet a certain per- 
centage of the population 
of any community may 

be found harboring the The record of Auburn, New York, is one that can be 

A mh +>. Pria ffPrm <? p 1 th m 1 trh attained in all towns. Diphtheria can be eradicated if 

aipntnena germs, aitnougn proper prophylactic mea sures are taken, 
unaware of having been 

exposed to any case of diphtheria. The germ of this disease 
grows freely in milk. As this food undergoes so much handling 
during production, the germs of diphtheria often have an oppor- 
tunity to get into milk unless great care is taken. 

The diphtheria germ is easily killed by ordinary disinfectant 
solutions and is rather easily killed by drying. When it is con- 
tained in pieces of membrane, it may live for some time. Heat 
quickly destroys the germ, but temperature as low as freezing is 
not fatal to it. 

Treatment. The communicability of diphtheria renders impera- 
tive the strict isolation of patients. Unnecessary furniture should 
be removed from the room, and that which is left should be of a 
kind easily cleaned. Separate linen and utensils of every kind 
should be provided for the exclusive use of the patient. Such 
materials should be boiled, or, better, treated with a powerful 
germicide after use. The attendant nurse and the physician 


should be the only persons in contact with the patient. After 
handling the patient, which should be done as infrequently as 

possible, the hands 
of the attendants 
should . be immedi- 
ately cleansed in a 
germicidal solution 
and then washed with 
soap and water. 

Diphtheria anti- 
toxin is usually ad- 
ministered early to 
help the patient get 
control of the disease. 
This antitoxin pro- 
duces immunity with 
little or no work on 
the part of the cells 

The strength of the toxin is tested by injecting a very small „ , , , . 

volume into a 250-gm. guinea pig. If the pig dies within four 01 the patient S body, 

days, it is toxic enough to inject into a horse to produce q •• . ... 

antitoxin. After a given time, blood is drawn from the horse, oUCh immunity IS 

the serum with its antitoxin is separated from the blood and U rir4 ,, rr , QC Q c " , p 

again tested. This time, a little serum is mixed with some Known ab pdSblve 

toxin and the mixture injected into a guinea pig. If the pig i m m n n t + v Wh p n 

lives, the serum is shown to contain antitoxin and will be eff ec- immunity. " ucu 

tive. Look up the exact amounts of material and time in- -fc\iQ antitoxin neU- 
volved in this standardization process. 

tralizes the toxins of 
the invading germs, the patient's body develops its own anti- 
toxins. This results in an active, permanent immunity. The 
administering of a sufficient quantity of antitoxin is the primary 
remedy for the cure of diphtheria. When a physician is not 
called early enough, the case may advance so far that the ad- 
ministration of antitoxin is valueless. Too much toxin has then 
been produced by the invading germs for the antitoxin to v neu- 
tralize. If other members of the family are in contact with the 
patient and have not been immunized by the toxin-antitoxin 


mixture, it is always advisable to give them an inoculation of anti- 
toxin, which will produce an immediate immunity for a short time. 

The application of the Schick test. By means of the Schick tests 
it is possible to determine which individuals possess immunity to 
diphtheria and which individuals are susceptible, that is, are likely 
to contract diphtheria if exposed to the germs. If a child is 
found to be susceptible, he is rendered immune by injections of 
toxin-antitoxin. This stimulates the body to produce its own 
antitoxins and thus establish an active immunity. 

The Schick test and the subsequent inoculations are invaluable 
in checking diphtheria. The reason for the presence of diphtheria 
to-day is probably because the inoculations are given to school 
children instead of children of pre-school age. The susceptibility 
to diphtheria is very low at birth, but it increases gradually until 
the individual is two or three years old, and then it starts to 
decrease. Probably not more than 12 per cent of adults are 
susceptible to the disease. Since the Schick test indicates the 
individuals who are not immune, preventive treatment, in the 
form of toxin- antitoxin, may be given to them. 

Diagnosis. The correct diagnosis of diphtheria plays a very 
important part in its control. Not only does the safety of the 
community depend on the detection and isolation of cases of diph- 
theria, but the early recognition of the disease diminishes the 
mortality because treatment is also earlier. The only dependable 
means of diagnosis is the microscopic examination of cultures 
obtained from the throat and nose. 

Prevention. Diphtheria has been responsible for the deaths of 
so many children that health authorities are trying to prevent the 
disease by completely eradicating it. If all school children should 
receive the Schick test and be immunized by the toxin-anti- 
toxin method, very few diphtheria cases would be found. This 
can only be made possible through an educational campaign, by 
means of which the people will understand the danger and char- 

WH. FITZ. AD. BIO. — 30 


acteristics of the disease, and the best methods of controlling 
it. If a physician is consulted as soon as suspicious symptoms 
appear, he can administer antitoxin immediately and probably 
prevent a serious case of the disease. Children should be taught 
to keep pencils and all articles handled by other children out 
of their mouths. Since diphtheria is a droplet infection, the 
same rules for prevention apply here as in other diseases spread 
by this means.- Patients who are convalescing from diphtheria 
should be kept away from well persons until all danger of spread- 
ing the infection is eliminated. 

Scarlet Fever 

Scarlet fever is a disease similar to diphtheria, in that it works 
through toxins. The causative organism has not been definitely 
isolated. A chain form of spherical bacteria called streptococci 
is always found in the nose and throat of scarlet fever patients, 
but there is considerable doubt as to whether this is really the 
causative organism. Seventy per cent of the deaths from scarlet 
fever are among children under ten years of age. 

A test, similar to the Schick test, has recently been prepared 
to determine the presence or absence of scarlet fever immunity. 
It was devised by two doctors, G. F. and G. H. Dick, and is 
called the Dick test It consists of putting small quantities of 
toxin prepared from the streptococcus bacillus under the skin of 
the child to be tested. There is a reaction similar to that in the 
Schick test. 

If a child is not immune, subsequent doses of toxin are inocu- 
lated. It is not necessary to neutralize the toxin with antitoxin 
as in the case of diphtheria, because the scarlet fever toxins are 
not as powerful as the diphtheria toxins. This inoculation cre- 
ates an active immunity in the child by stimulating its body to 
make its own antitoxins. The Dick test and its subsequent in- 
oculations are not used to the extent of the Schick test and inoc- 



illations, but its use seems to be growing constantly. There is 
also an antitoxin for scarlet fever. It is prepared from the 
horse's blood in a way similar to the preparation of diphtheria 
antitoxin. It has been used with considerable success to pro- 
duce an immediate immunity in case the child is in the initial 
stages of scarlet fever. 

The method of transmission of scarlet fever is through droplet 
infection similar to that of diphtheria. 

Tetanus (Lockjaw) 

Tetanus, a disease that develops from the germs entering a 
deep injury or wound, is due to the action of the toxins of a par- 
ticular microorganism. These toxins affect the brain and spinal 
cord. No noticeable effect is produced in the wound through 
which the germ enters. Fortunately, tetanus is rare in this coun- 
try, but when it does occur *the death rate is very high. The 
extensive prevalence of tetanus among the soldiers wounded in the 
late World War was ascribed to 
the contamination of their wounds 
with soil from a highly cultivated 
territory which had been regularly 
and frequently fertilized with 
manure. This soil contained the 
germs of the disease. 

Cause. This disease is caused 
by the tetanus bacillus, a rod- 
shaped microorganism which grows 
in long, slender threads. These 
threads break up.,, into shorter 
motile rods surrounded by fla- 
gella. These bacilli eventually be- 
come non-motile, lose their flagella, and each forms a spore at one 
end. This gives to them their characteristic drumstick appear- 

Certain bacteria roll themselves up in- 
side a thickened wall to form a spore. In 
the photomicrograph of the tetanus organ- 
isms the spore appears at one end of the 


ance. Under favorable conditions these spores remain virulent for 
years. The tetanus bacillus was first discovered by Nicolaier in 1884 
and cultivated by Kitasato in 1889. Shortly after this, Von Beh- 
ring succeeded in producing an effective tetanus antitoxin. 

Occurrence. Tetanus bacilli are found in damp soil and in dust, 
especially around stables, in manure, and in dust of the house and 
street. They are so plentiful in the intestinal contents of horses 
and cows, whose wastes are commonly employed to fertilize gar- 
dens, that tetanus is sometimes regarded as a disease contracted 
indirectly from these animals. Other herbivorous animals also 
harbor the germ. The bacilli are likely to be found on rusty nails 
or implements which have been in contact with the ground, on 
dirty splinters, and* on gunshot. 

Tetanus bacilli are anaerobic (cannot grow when exposed to 
the air) ; therefore, deep wounds are most favorable for their de- 
velopment. They are unusual in that they do not grow on healthy 
living tissues, but on cells which have been torn and killed. Badly 
lacerated wounds present a more favorable surface for the growth 
of tetanus than do those made by very keen clean instruments. 

How tetanus enters the body. The bacilli gain entrance to 
the body through wounds varying in size from a needle prick to 
an operation wound. Being anaerobic, the organisms infect 
deep lacerated wounds such as those made on the hand by the 
accidental explosion of a toy pistol or wounds on the feet made by 
the deep puncture of a rusty nail. Rusty nails themselves never 
produce lockjaw, but the bacteria are frequently held in the rough 
spots of the rust and consequently enter the body if the nail 
happens to puncture the flesh. Occasionally, the disease occurs 
without any evident wound. In cases like this, the bacteria have 
made an entrance through some unnoticed abrasion of the skin or 
the mucous membrane. 

Tetanus has been observed not only in man, but in domesticated 
animals such as the horse, sheep, dog, cow, and pig. 


The nature of the disease. The effects of the disease are due 
to the action of toxins produced by the bacilli upon the central 
nervous system. The bacilli themselves apparently do not move 
from the deep seated area of entrance. The symptoms of tet- 
anus are usually noticeable any time from two to nine days 
after a wound has been received. The bacillus which entered the 
wound as a spore may require some time to become active again. 

Treatment. When the organisms have once started to produce 
their toxins, hope of controlling the disease is only slight. The 
toxins, even though present in the minutest amount, are so very 
poisonous to certain parts of the brain and spinal cord that all efforts 
to neutralize or counteract the activity are usually of no avail. 

Whatever treatment is given must be early. Wounds likely 
to be contaminated with tetanus, as those into which soil 
may have entered, or gunshot wounds, should be opened and 
washed with a strong antiseptic. If the danger of infection is 
considerable, the wound should be cauterized. In addition to 
this, a dose of tetanus antitoxin (antitetanic serum) ought to be 
administered. When precautions have not been taken and " lock- 
jaw " sets in, the serum injected into the spinal canal sometimes 
brings about the desired result. 

Tetanus antitoxin. Certain State Departments of Health pre- 
pare antitoxin to be used both in the prevention and in the treat- 
ment of the disease. Tetanus bacilli are grown in broth, away 
from the air. The resulting liquid, loaded with tetanus toxin, is 
filtered gradually and injected at intervals, in increasing amounts, 
into the veins of a horse. Later, a large amount of blood is drawn 
from the animal and the serum is separated. This serum con- 
tains antitoxin which has been produced in the horse to neu- 
tralize the introduced toxin. The serum is known as the anti- 
tetanic serum. The antitoxin has a high preventative but a low 
curative value. Its production is in many ways similar to that 
of diphtheria antitoxin. 


Prevention. Care should be taken to avoid cuts and wounds of 
all kinds, especially from objects soiled with manure or fertilized 
soil. The restriction of the use of fireworks during the past few 
years has very markedly reduced the number of cases of tetanus 
occurring over the country at large. All gunshot and " Fourth 
of July " wounds, any extensive or deep wounds, and every form 
of punctured wounds should receive care from a physician. Where 
such wounds have had dirt driven into them, the desirability of 
an injection of tetanus antitoxin is very great. The antitoxin 
must be given early as it is preventative and not a cure of 
tetanus. Wounds suspected of containing tetanus organisms 
should be opened and thoroughly cleaned. Gauze bandages, 
which are porous, should be used, never air-tight bandages. 

Questions and Suggestions 

1. Discuss the discovery of the causative organism of diphtheria. 

2. Discuss the work of Emile Roux. 

3. Review and report on the work leading to the discovery of 

4. Contrast active and passive immunity. 

5. Discuss the Schick test and its importance. 

6. How do diphtheria bacilli gain entrance to the body ? 

7. How do diphtheria bacilli attack the body ? 

8. What educational propaganda for parents is still necessary be- 
fore diphtheria can be eradicated ? 

9. Contrast and compare scarlet fever with diphtheria in cause, 
prevention, and treatment. 

10. Explain why the prevention of a disease is more to be desired 
than the cure. 

11. What is the similarity between tetanus and diphtheria? 

12. Where are the tetanus bacilli found ? 

13. What is the relation of tetanus to different types of wounds ? 

14. Is there any truth in the belief that one will surely get tetanus 
if he cuts himself between the thumb and first finger ? 

15. Why are tetanus organisms found in dirty places more commonly 
than diphtheria or scarlet fever organisms ? 

16. What has caused the reduction in the number of deaths from 
tetanus ? 


17. How should a wound be treated if there is any possibility of 
tetanus infection ? 

18. Look up and report on the life and work of Loeffler and of 
Von Behring. 

19. Look up the health bulletin of your village, city, or state and 
plot a curve of the number of cases of tetanus reported annually for 
the last ten years. Were any of the cases fatal ? 

Supplementary Readings 

Broadhurst, J., How We Resist Disease (J. B. Lippincott Co.). 
De Kruif, P. H., Microbe Hunters (Harcourt, Brace & Co.). 
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.). 
Rosenau, M. J., Preventive Medicine and Hygiene (D. Appleton & Co.). 

-*•< : ^ .,«. . +- 

%*r' ^^ /**%. 


Bacterium typhosum 

Some have flagella 

What is the danger of typhoid infection in the United States f What are 
some of the measures of preventing typhoid infection f Why are oysters 
a greater source of contamination than milk, in some cities f 

Prevalence of typhoid fever. During the Spanish-American 
War typhoid spread rapidly through the embarkation camp in 
Florida. More men died of fever than were killed in battle. 
During the South African War, the British army lost 7582 men 
from wounds and 8225 from typhoid. To-day, all soldiers in our 
army are required to be vaccinated against typhoid fever; and 
typhoid is probably rarer in military camps than in the most 
healthful cities and towns. Formerly, the death rate of typhoid 
in the United States was forty per 100,000. In the last few years 
this number has been reduced to four per 100,000. 

Since the World War, the death rate from typhoid has been re- 
duced most among men between 29 and 45 years of age. This 
is largely due to the education and practice in disease prevention 
by vaccination given to the millions of men who were in the army. 

Cause. Typhoid is due to a small, motile, rod-shaped bacte- 
rium, the typhoid bacillus. It is short, probably about one half 
the length of the diphtheria bacillus. 

Nature and symptoms of typhoid fever. The disease is located 
primarily in the lining of the intestine. The germs then pene- 



trate the lining and enter the blood stream. The increased ac- 
tivity of tissue cells in combating the germs and their toxins causes 
fever and the whole body suffers. Convalescence sometimes re- 
quires many weeks. Mortality from typhoid fever is about 10 per 
cent. From two to four per cent of all persons who have had 
typhoid are typhoid carriers for some time after recovery. This 
condition may become chronic and remain for years. 

One typhoid carrier is reported to have been responsible for 
several outbreaks of the disease. He infected 30 persons, 5 of 
whom died. Another carrier was a cook who had prepared a large 
dish of spaghetti for a dinner. Subsequently, 93 people who 
attended the dinner became ill with typhoid. There is a similar 
historic case in New York city. " Typhoid Mary " was a cook 
and had worked in various families. She had never had the dis- 
ease but carried the germs. Fifty cases of typhoid were traced 
to her. Since her entire history is not known, she may have 
been the cause of many more cases of typhoid. Shie has finally 
been confined and her personal habits supervised very carefully to 
prevent any further contagion. Because of the danger from car- 
riers, the Health Department of various cities and states requires 
a thorough physical examination "of all people who handle foods. 
This law has resulted in discovering several typhoid carriers and 
placing them under strict supervision. 

Protection of the body against typhoid. The germs of typhoid 
produce powerful endotoxins, toxins within the cell. The body 
fortifies itself by producing various protective materials, some 
of which dissolve the invading germs and are known as bacteri- 
olysin. The body cells also produce chemical substances, called 
agglutinins, which cause the germs to be surrounded by a gluelike 
substance. This results in a clumping or agglutinating of the once 
motile germs of typhoid. When these bacteria are stationary and 
in masseS? instead of moving around, the white corpuscles can 
more readily devour them. The presence of agglutinins can be 



determined by adding blood of a patient who has typhoid, or 
has recently had it, to some typhoid bacilli on a glass slide. 

cover- -slip ...Tiangi ng "&rop 


? / \ K- o 

/ \ 

' ^ \ ^ 

'K \ ' ^ 

; N - v / 

The diagram on the left, shows free swimming typhoid bacilli. The one on the right, shows 
typhoid bacilli clumped in masses by the presence of agglutinins from the blood of a typhoid pa- 
tient. The agglutination test is usually made in a hanging drop on a glass slide as shown above. 

When this drop is viewed under the microscope, the germs are 
seen clumped together in masses. 

One attack of typhoid produces immunity. This is probably due 
to the fact that so much protective material is developed to combat 
the powerful typhoid toxin that much is left over and stays in the 
blood for life. Since the toxin is not an exotoxin as in diph- 
theria, antitoxin would be valueless and probably is not produced. 
The body combats a disease germ which produces an endotoxin 
by fighting the actual germs with their inclosed toxins. 

Diagnosis. As early a diagnosis as possible must be made if 
the patient is to get the best possible treatment. An early quar- 
antine must be established to prevent the spread of the disease 
to other people. 



One method of diagnosis is the examination of cultures, made 
from the feces (excreta) of the patient, for the presence of typhoid 
germs. Doctors take samples of fecal material from the patient 
and send it to the Board of Health laboratories. There the ma- 
terial is mixed with media and the developing bacterial colonies 
are examined for typhoid bacilli. 

Another method of diagnosis is the Widal test. This con- 
sists of separating serum from the patient's blood and mixing 
it with a culture of known typhoid germs. If the patient has 
typhoid, the blood serum will cause the germs to become ag- 
glutinated. Agglutinins for typhoid are present in the blood 
only when typhoid bacilli are in the body or if a person has 
recently recovered from typhoid. The Widal test is a means of 
differentiating typhoid fever from other diseases that produce 

Method of Spread. Typhoid germs are spread largely through 
materials contaminated by the excreta of typhoid patients. This 
may be, and most frequently is, water which has been polluted by 
sewage and milk which has 
become infected probably 
by being kept in containers 
which have been washed in 
polluted water. Raw foods 
such as oysters, if they 
are grown where they come 
in contact with sewage, 
may cause typhoid fever. 
Raw foods such as celery 
and lettuce, which may 
have been watered or 
washed with contaminat- 
ing water, are frequently carriers of the disease. Insects, princi- 
pally the house flies, which travel readily from filth to exposed 



• : 

4 ■; 'V ■ 

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Agglutinins of various types may be present in the 
blood. The picture on the left shows agglutinated 
typhoid bacilli, on the right agglutinated pneumonia 


foods, are notorious carriers of typhoid germs. Human beings 
may also carry and transmit the germs. 

Prevention. Typhoid fever can be prevented both by keeping 
the typhoid bacilli from entering the body, and by destroying the 
bacilli. Since typhoid germs are spread by materials polluted by 
human excretions, or by the housefly, or a human carrier, some of 
the methods of preventing a typhoid outbreak are the following : 

1. Disinfect all excreta of typhoid patients or carriers with 
chloride of lime. All clothing and bed linen of a patient should 
be disinfected by being boiled or soaked in carbolic acid or bichlo- 
ride of mercury solution. 

2. Provide a good sewage system. 

3. Provide a good water supply. Chlorinate the water. (Boil 
the water if an infection is suspected.) 

4. Pasteurize all milk, or require such sanitary milking condi- 
tions that pasteurization is unnecessary. Following the introduc- 
tion of pasteurization of milk in several cities in 1914, there was a 
marked decrease in typhoid. 

5. There should be proper handling of foods in the grocery, in the 
market, and in the home. Food should be properly covered and 
protected from flies. Foods which have been exposed should be 
thoroughly washed. 

6. Health certificates should be required from persons who 
handle foods in order to eliminate the danger of typhoid carriers. 

7. There should be a proper control of the house fly. The de- 
struction of their breeding places, keeping the premises clean and 
garbage covered, screening the houses, and screening the sick- 
rooms will help exterminate the house fly. 

8. Vacationists, nurses, doctors, and any other people who are 
likely to be exposed to typhoid infection or unsanitary conditions, 
should be vaccinated. People may be immunized at any clinic, 
providing they cannot afford to have their own doctors immunize 
them. The immunity usually lasts from two to four years. 



Vaccination. Immunity to typhoid may be gained artificially 
through vaccination. In the case of smallpox vaccine, the germ 
material was weakened through cultivating it in animals. In 
preparing typhoid vaccine, the bacilli are first grown on agar, 
then killed by heat, and a little carbolic -acid is added to the vac- 
cine for a preservative. When this material is used as a vaccine, 
the presence of the dead bacilli stimulates the body to make bac- 
teriolysins and agglutinins. Thus a vaccinated person is pro- 
tected against the invasion of living germs. Usually three 
inoculations of vaccine are given, each being seven days apart. 

Very few people are made ill by typhoid vaccination. If the 
person is likely to come in contact with paratyphoid, which is a 
disease somewhat similar to typhoid, 
he is given a combination vaccine of 
typhoid and paratyphoid. For most 
people living in the United States 
or visiting here, the typhoid vaccine 
is sufficient, because there are few 
cases of paratyphoid in the United 

The investigation of a typical epi- 
demic. During November, 1924, there 
was a noticeable rise in the number 
of typhoid fever cases in New York 
city. This continued through January, 
1925. Of the 914 cases recorded in 
this outbreak, 116 of the residents, and 
59 nonresidents who were included 
in the 914 cases, gave a history of 
having been out-of-town during the 
period immediately before their illness. 
The majority of these had eaten oysters while out-of-town. About 
18 per cent of the cases probably acquired their infections in 



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Bacterium coli. 

These organisms are commonly 
present in the intestine of man. 
Their presence in swimming pools 
indicates the possibility of contami- 
nation by human excreta. This 
might also indicate the possible 
presence of typhoid bacilli. Bac- 
teriological examinations of water 
in swimming pools are frequently 
made to determine the presence of 
bacterium coli. Their presence 
would make the closing of the pool 
imperative until proper prophylactic 
measures were taken. 



this way, but that did not explain the cause of the other cases, so 

the investigation continued. 
The water supply of most cities is constantly tested for bacillus 

coli, a microorganism found in all human intestines. If the 

bacilli coli are 
present, there is 
the likelihood of 
typhoid also being 
present. The 
water of many 
cities is chlorinated 
and this results in 
purification. The 




civil. Spanish - World 


A surgeon general of the U. S. Army has compared the death bacilli Coli are 
rates of men treated in hospitals for typhoid, during the first two . ■. , 

years of three different wars. The diagram indicates the number practically never 

of deaths in every iO.000 cases. ^^ ^ ^^ 

which is thoroughly chlorinated. Since the water supply was 
chlorinated, it could not have been responsible for this epidemic. 

The milk supply was investigated and nothing definite was 
found. The investigators paid particular attention to milk, 
because in 1913, before pasteurization, an infected milk supply was 
responsible for 521 cases and 61 deaths from typhoid. Ice 
cream, water ices, and bottled water supplies were investigated. 
Again there was no evidence of infection. Uncooked foods, par- 
ticularly lettuce and celery, were scrutinized with care. No 
worthwhile evidence was revealed there.. 

The first bit of evidence was that a great number of the re- 
maining cases gave a history of having eaten oysters approxi- 
mately two weeks before the onset of the symptoms. Fifty-five 
per cent or 506 cases gave a definite history of having eaten 
oysters. In April, 1915, a similar condition had existed. In an 
outbreak of 150 cases, 80 per cent seemed to be due to the use 
of raw oysters. Even when oysters are grown in clean, unin- 


fected water, they are frequently contaminated by the people 
who gather, ship, or otherwise handle them. The same safe- 
guards which have been established to protect milk from pollu- 
tion at each and every stage of its handling must be exercised 
in the handling of oysters. 

A number of the remedies have been suggested in order to pre- 
vent similar epidemics of typhoid fever. The shores and water 
that have been set apart for oyster beds should be constantly 
guarded and examined. Sewage and the contents of cesspools 
should not be emptied near them. Boats, both pleasure and Com- 
mercial, should be prohibited in such districts. Oysters from a 
polluted stream should not be transplanted. The gathering, pack- 
ing and shipping of all shellfish should be efficiently supervised, 
and the people who handle them in any way should receive fre- 
quent and thorough examinations. 

In the summer of 1928, tests were made of the waters of vari- 
ous bathing beaches near different cities and in many cases the 
water was found to be polluted. The Commissioners of Health 
suggested that bathing be prohibited in these places. This was 
not done as certain authorities claimed that the value of the sun- 
shine and bathing was so great, and that it was so possible and 

In New York city there has been a steady decrease of deaths from typhoid fever since pas- 
teurization of milk has been required. 


easy to secure immunity from typhoid fever by vaccination, that 
all bathers should be immunized and thus be protected. Many 
followed this suggestion. It is always advisable for bathers usin& 
water that may become contaminated to be vaccinated. In this 
way such recreation will be healthful as Well as pleasurable. 

Questions and Suggestions 

1. Compare typhoid fever statistics in the Spanish- American 
War and the World War. 

2. Discuss the dangers of typhoid carriers fo a community. 

3. Name two antibodies produced by the body as protection 
against typhoid. Discuss the importance of each. 

4. Discuss the relation of white corpuscles to combating typhoid 
in the body. 

5. What is the value of an early diagnosis of typhoid fever ? 

6. Describe two methods used in accurately diagnosing typhoid. 

7. How is typhoid fever spread ? How can it be prevented ? 

8. Explain the preparation and use of typhoid vaccine. 

9. Discuss how an investigation of a typhoid epidemic is carried on. 

10. Why is it unwise to drink water from springs within city limits ? 

11. Why is the water of swimming pools constantly tested ? What 
does the presence of bacilli coli indicate ? 

12. Why is it more important for a traveler to have typhoid vac- 
cination than for one staying at home ? 

13. Discuss any epidemic of typhoid that has been in your home 
town or city. 

Supplementary Readings 

Broadhurst, J., How We Resist Disease (J. B. Lippincott Co.). 
Dublin, L. I., Health and Wealth (Harper & Bros.). 
Meredith, F. L., Hygiene (P. Blakiston's Son & Co.). 



^Hf* - Jf:\ ft '" 



A ' , 



Fleas may carry bubonic 

The louse may carry typhus 

i/ow mai/ co/ds 6e prevented f Have colds any serious effects on the 
body? Is there any relation of asthma to food? Is it possible or 
desirable for children to avoid the so-called children's diseases ? 

Causes of colds. It is generally conceded that there are two 
types of inflammation called colds. The first type is caused by 
bacteria and is a real infection. The germs may attack a certain 
local area, thus causing a cold in the head, a sore throat, laryngi- 
tis, or tonsillitis, or they may have general widespread effects as 
in grippe. The second type of cold is caused by physical agents 
such as irritant gases or dust. Colds and even pneumonia have 
been caused by breathing in talcum powder. Dust inhaled in 
working at trades such as diamond polishing, metal polishing, or 
marble quarrying may cause colds, followed by pneumonia, or 
tuberculosis. It is the physical material which starts the irrita- 
tion, then bacteria enter the irritated tissues and set up infections. 
Other factors that may cause colds are dry heated air, drafts, 
sudden changes of temperature, exposure to cold and wet, im- 
proper food, and constipation. 

Effect of colds on the body. Bacteria causing colds are usually 
present in the mucous membrane of the nose, mouth, and throat. 
When the resistance of the body is lowered, it is thought that 

WH. FITZ. AD. BIO. — 31 



these bacteria gain a foothold and produce the condition known as 
a cold. Blood congests in the mucous membrane which becomes 
swollen and causes a profuse flow of mucus. The mucous mem- 
brane of the tear ducts may also swell and the tears will flow con- 
tinuously. If the inflammation spreads to the Eustachian tubes, 
they may become closed and hearing is temporarily impaired. If 
the infection extends to the middle ear, earache usually results. 
Sometimes infection may extend to the cavities in the bones of 
the front of the skull called the sinuses and cause inflammation 
or sinusitis. If the infected material is retained in the sinus, the 
condition usually becomes chronic. 

A chronic cold is known as catarrh. If the disease extends 
down into the bronchial tubes, the condition is known as bron- 
chitis ; the inflammation of the finer bronchi may cause broncho- 
pneumonia. People who work indoors and at sedentary occupa- 
tions are more likely to suffer from colds than persons who live an 
outdoor life, as dust, dry air, and noxious gases are continually 
irritating the respiratory tract and making it susceptible to infec- 
tion. These same predisposing factors increase the likelihood of 
the disease extending into broncho-pneumonia. This type of pneu- 
monia is unlike lobar pneumonia. The latter is caused by a specific 
microorganism, the pneumococcus. Broncho-pneumonia may be 
caused by any bacteria that infect the bronchial tubes and air 

Colds are frequently neglected and considered of trivial im- 
portance. Each cold lowers the resistance and vitality of the 
body to such an extent that the sufferer is likely to contract other 
infections. This may hasten the progress of a serious disease like 
tuberculosis. Every effort should be made to prevent colds. Once 
a cold is contracted, the best possible care should be taken to 
avoid any secondary infections. 

Method of spread. Even with many of the predisposing fac- 
tors present, a cold does not develop unless there is an exposure 


to infection from another person who has or is just recovering 
from a cold. Sometimes the infection already exists in the indi- 
vidual in a chronic but extremely mild state, and it may become 
acute when the vitality or resistance is lowered. Eskimos and 
Arctic explorers, in spite of the severe weather conditions, do not 
have colds. When such explorers return to civilization they may 
be infected by droplets sprayed by the coughing and sneezing of 
people whom they meet, and they soon experience a severe cold. 

Prevention of colds. Since a cold is a droplet infection, it 
generally travels through the sputum. Crowds in ill ventilated 
places should be avoided. The germs can live only for a very short 
time in air. Their culture medium is the air passages of human 
beings. In crowds, it is impossible to avoid the sneezing or 
coughing of other people. That is the way colds are spread and it 
is the reason for the frequency of colds. Spitting spreads sputum- 
laden bacteria into the air. If a person talks directly into the face 
of another person, droplets of sputum are given off and inhaled. 

An experiment was made in England to show that droplets 
from the mouth are spread. A certain member of Parliament was 
asked to wash out his mouth with a culture of harmless bacteria 
which, when plated, produce red colonies. He then made a loud 
and eloquent speech. Petri dishes had been distributed in all 
parts of the House of Parliament, even to the rear of the gallery. 
When gathered, incubated, and the plates examined, all the ex- 
posed dishes contained red colonies. The closed controls showed 
none. The speaker had showered the entire house with micro- 
scopic droplets containing the harmless bacteria. 

Coughs and sneezes must be covered in order to prevent the 
spread of infections. When a person has a cold, he should use 
gauze instead of handkerchiefs and the used gauze should be burned. 
Some people seem to be more susceptible to colds than others. 
This may be due to abnormalities in the nose or throat. Ade- 
noids and infected or enlarged tonsils are excellent locations for 


the harboring and growth of germs, and should be removed. 
Teeth should be straightened so that correct breathing will be 
possible. Nasal douches should not be used regularly, as the 
solutions used in them may be irritating to the delicate mucous 
membranes, and may cause an infection. If the nasal passages 
are in healthy condition, strict observance of the rules of individ- 
ual hygiene is likely to prevent colds. Living and sleeping out- 
of-doors will keep fresh air in the lungs and will prevent colds. 
Children with colds should be kept home from school in order to 
keep the infection from spreading. 

Remedial measures. A cold is very likely to run a regular 
course, although proper treatment may relieve some of its un- 
pleasant features. The patient should avoid drafts and keep warm. 
If it is possible to stay in bed for a day, many of the symptoms 
can be mitigated. A hot foot-bath, hot drink, and massaging 
the neck and chest well just before going to bed are often very 
beneficial. These measures help in stimulating circulation and in 
breaking up the congestion. If the weather is mild and sunny, 
the patient should spend as much time as possible out-of-doors. 
There are special vaccines prepared against colds and used with 
some slight degree of success. They are sometimes successful in 
stimulating a person's body to work up an immunity. 

Influenza. Epidemics of influenza have spread all over the 
world, therefore, it is frequently called a pandemic disease. In- 
fluenza of the respiratory tract is the most common form of the 
disease, although there are other forms. It usually starts with a 
cold, followed by a high temperature and extreme weakness. It 
may extend into the lungs and cause bronchitis or pneumonia. 
The disease is spread by direct contact. The secretions of the 
mouth and nose carry the infectious agents. Droplet infection 
is generally considered to be the method of spreading influenza. 
Unlike many other diseases, one attack does not usually establish 
an immunity. 



Asthma. Any condition of difficulty in breathing is popularly 
known as asthma. Some conditions of asthma are due to lung 
infections, others to food poisoning. If cer- 
tain foods disagree with a person, the reaction 
may be shown by an asthmatic condition. 
Frequently, rashes are caused by a sensi- 
tivity to certain foods. In order to discover 
what food is causing the reaction, different 
foods are injected below the skin. If the skin 
shows irritation, the food causing it is taken 
from the diet and the asthma often clears up. 

When a plant pollen causes asthma, it is 
known as hay fever. Vaccinations of pollen 
are inoculated into the skin to see which of 
the pollens cause the sensitivity. The pollen 
from the ragweed is responsible for many cases 
of hay fever. When the right pollen is de- 
termined, small quantities of it are inoculated 
into the sensitive person until he works up 
an immunity. Up to the present time these 
vaccinations have not always proved suc- 

Focal infections. Bacteria at some point 
or focus in the body frequently, multiply and 
produce toxins which are absorbed into the 
body and affect other parts. When people 
tire easily, lack normal energy, and are 
subject to pains in the joints and muscles, 
they may have a focal infection. Other 
evidences of focal infections are inflammatory 
rheumatism, heart disease, kidney disease, lumbago, and nervous 
conditions such as neuritis and neuralgia. 'When any of these 
conditions occurs, the doctor usually looks for a focal infection. 

Skin tests may be made 
to determine an individ- 
ual's sensitivity to differ- 
ent foods. Small volumes 
of different foods are in- 
jected under the skin or 
small amounts are rubbed 
into tiny gashes made on 
the arm. One cut, the 
control, is not treated with 
food. Little or no red- 
ness or soreness is pres- 
ent near the control. 
Varying amounts of in- 
flammation appear about 
the infected areas. Red- 
ness and soreness denote 
a positive reaction and 
indicate sensitivity. 


Common foci of infection in the body are diseased tonsils, 
chronic infections of the ear and nasal cavities, which may spread 
to the sinuses, pockets of pus about the roots of the teeth, and a 
diseased appendix. When the focus of infection is removed, the 
symptoms tend to disappear. Regular and systematic care of 
the teeth by a competent dentist, with the use of X-rays when- 
ever possible, will bring to light pus pockets in teeth. Avoidance 
of, and proper care of colds will prevent sinus and ear infections. 
Regular periodic health examinations will usually detect these 
foci of pus before they cause disease in the body. Once a focal 
infection is started, it may be very difficult to cure it. 

Measles, whooping cough, and chicken pox. These diseases 
are common among children because they are spread through the 
unhygienic habits that are prevalent among all children. When 
a little girl hugs another one, takes a bite of her apple, borrows her 
pencil, or performs endless other acts that result in personal con- 
tact, disease germs may be passed from one child to the other. 
In some households, if one child contracts one of these diseases, 
all the children of the family are purposely exposed to it. It is 
easier to take care of all at the same time. This is a very wrong 
procedure. These diseases, in themselves, are not very serious 
and seldom fatal. But they are frequently followed by secondary 
infections such as pneumonia, deafness, rheumatism, heart disease, 
or kidney disease. The after-effects are far more serious than 
the original disease. When one child gets a disease from an- 
other, the second child may get it in a more severe form than the 
first. In growing in the first child's body, the disease germ seems 
to acquire greater virulence and, consequently, affects the second 
child more seriously. Either this is the case or weaker strains of 
bacteria are killed in the first child's body and only those virulent 
organisms that are resistant to the defenses of the child's body are 
passed on. Children who show any signs of illness should remain 
home from school until they are again perfectly well. Because 


they can stay out in the sunny open air, if well enough, or relax 
in bed, their recovery will be hastened, and they will not spread the 
infection through the school. 

Questions and Suggestions 

1. Discuss the causes of different kinds of colds. 

2. What effects have colds on the body ? 

3. How are colds spread ? 

4. How can the vitality of the body be kept high so that colds may 
be prevented ? 

5. What unhygienic practices have you noticed among students 
which may account for epidemics of colds in a school ? 

6. How can epidemics of colds in schools be prevented ? 

7. Compare influenza to an ordinary cold. 

8. Discuss the common causes of asthma. 

9. What do asthma vaccinations consist of? 

10. Discuss focal infections and their relation to the health of the 

11. What is the relation of so-called children's diseases to the vital- 
ity of a child ? 

12. Discuss some after-effects that may result from measles, 
whooping cough, and chicken pox. 

Supplementary Readings 

Broadhurst, How We Resist Disease (J. B. Lippincott Co.). 
Haggard, H. W., The Science of Health and Disease (Harper & Bros.). 
Rosenau, M. J., Preventive Medicine and Hygiene (D. Appleton & Co.). 





Walter Reed. 

Underwood & Underwood 
Hideyo Noguchi. 

How has malaria been controlled? Why ivere the French unable to 
build the Panama Canal f Who was Hideyo Noguchi? 

Malaria is caused by a microscopic protozoan, known as a 
Plasmodium. There is some discussion as to whether the organism 
that produces yellow fever has really been isolated. 

Prevalence of malaria. In 1908 there were more than three 
million deaths from malaria in India. Along the rivers and 
coasts of tropical countries, malaria is the white man's greatest 
obstacle to settlement. In temperate climates such as the 
L T nited States malaria is not usually fatal, but in the tropical 
countries it occurs in most severe forms and the death rate is 
very high. 

The use of the drug, quinine, is most effective in treating malaria, 
since it kills the malaria protozoans in the blood. In 1902, the 
Italian government began the sale of quinine at low prices to 
certain communities. This drug was distributed free to those 
unable to purchase it. In 1904, the Italian towns gave it to all 
working people. In consequence, there has been a progressive 
reduction in the amount of malaria in Italy. During the ten 
years previous to 1902, Italy averaged 14,048 deaths per year from 
malaria. In the nine years following 1902, the average fell to 3853. 




Fifty years ago malaria was so common in our Middle Western 
States that it was a serious problem. But this malady has grad- 
ually been reduced by scientific control. 

Malaria is still fairly common in the tropical countries. It 
was recently estimated that, approximately, 90 per cent of the 
people of Calcutta are suffering from this disease. 

History of malaria. The ancient Greeks thought that malaria 
was due to bad air arising from the marshes. Hence they called 
the disease malaria, which means bad air. Malaria always pre- 
vailed near swamps and was thought to be caused by some kind 
of emanation from decaying matter. In 1880, a French army 
surgeon, Charles Laveran, noted and described the malarial para- 
sites in the red corpuscles of the blood of persons suffering from 
malaria. But he was not able to ascertain how they entered the 
blood. This was not learned until 1895, by Major Ronald Ross, 
an English army surgeon, who started investigating malaria in 
India, where malaria was prevalent and existed in its worst form. 
Discovering that birds were 
susceptible to malaria, he 
first studied the organisms in 
the blood of the birds. He 
suspected that this disease 
was not contagious but was 
transmitted by the bite of a 
mosquito, and he permitted 
mosquitoes of a certain spe- 
cies to bite infected birds. 
He killed the mosquitoes, 
and found little swellings in 
the walls of their stomachs. 
Then he let similar mosqui- 
toes bite birds that were not infected with malaria, and no such 
swellings appeared in the stomach walls. He continued examin- 

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to ■ «o 

40 - 60 
60 • .80 
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"Mbr-taUty from >Talaria in ttakr 

Am. Museum of Nat. Hist. 
The Italian government has steadily decreased 
the cases and deaths from malaria. 


ing many of these small swellings in the stomach of the mosquitoes 
and found that they contained numerous parasites. When the 
swellings reached a certain size they would burst and the parasites 
were scattered through the mosquito's body. Some entered the 
salivary glands. Ross concluded that these parasites in the saliva 
of the mosquito would pass into the blood of the bird when the 
mosquito bit the bird. 

Cause. Malaria is caused by a protozoan parasite, Plasmodium 
malariae, somewhat like the amoeba. It has two hosts : the 
female mosquito of the genus Anopheles, and man. There are 
really three different types of malaria, caused by three different 
but related microorganisms. Malaria occurring in our latitude is 
a mild form of the disease. 

Spread. The germ of the disease is spread by the bite of the 
female Anopheles which has previously bitten a malarial patient. 
(The male feeds on plant juices.) The common mosquito, 
of the genus Culex, does not transmit malaria or yellow fever. 

Life history of the malaria parasite, Plasmodium malariae. The 
amoeba-like organism of malaria cannot complete its life history 
in the blood stream of man alone ; it requires two hosts, the mos- 
quito and man. Germs are injected into man through the bite of 
an infected mosquito. They enter the red blood corpuscles and 
multiply there, finally forming from six to sixteen spores. At inter- 
vals of 24, 48, or 72 hours, depending on the type of malaria, the 
spores, having destroyed the corpuscle, escape into the blood 
stream. The sudden release of these poisons, and the subsequent 
rallying of the body in an effort to counteract them, are thought 
to cause the chills and then the fever which are characteristic of 

Each escaped parasite now fastens itself to another red cor- 
puscle, enlarges, forms spores, and having used up and disinte- 
grated the corpuscle, again is set free, not as one but as many 
parasites. The cycle is repeated over and over again, until the 


patient recovers or succumbs. Some of the parasites undergo 
certain changes which differentiate them into sex cells. Since all 
the parasites were injected into the blood at approximately the 
same time, and since it takes each one just so long to grow, form 
spores, excrete wastes, and escape from the corpuscle, all, with 
their wastes, are ejected into the blood stream at one time. 
Therefore, the chills and fever occur at intermittent periods. 

When a mosquito bites a patient, it takes in the malarial 
patient's blood with the plasmodia which developed into two 
types of sex cells. These undergo divisions and changes. Study 
the diagram (p. 484) and note that some cells take different forms. 
Some of them become male cells, others, female cells. Fertiliza- 

etxle^c moscjvcito 

anopheles moscjuitd 

Culex, the house mosquito, differs in appearance from Anopheles, the malarial mosquito. 
Compare the different stages of growth in the life of these two insects. 

tion occurs in the stomach of the mosquito by the union of the 
male and female plasmodia. The fertilized cells bore into the 


wall of the stomach and form cysts on the outer stomach wall. In 
these cysts, the parasites break into thousands of needle-shaped 

spores, which finally 
escape from the cysts, 
enter the blood of the 
mosquito, make their 
way around the body, 
and especially infect 
the salivary glands. 
When the mosquito 
now bites another per- 
son, malarial organ- 
isms enter the victim's 
body with the mos- 
quito's saliva. The 
malarial parasite 
seems to produce no 
ill effects on the mos- 
quito. In the human 
host the malarial para- 
site reproduces asexu- 
ally and differentiates 
into sex cells which 
may be called a sexual 
phase ; in the body of 

The malarial parasite undergoes a cycle in its life history ±U~ mn«srmi+n it ror»rn 

from mosquito to man and back again to the mosquito. U1C 111US 4 U1LU 1L ii^wn 

Trace the complete history of the organism in the diagram duces both SeXUallv 

and asexually. 
Nature. The poison produced by the germs causes a marked 
chill, followed by fever, then profuse perspiration, and a fall of 
temperature. This is followed by a period of well-being until the 
onset of the next chill, usually 48 hours later in our type of 
malarias Destruction of the red corpuscles may cause anaemia 



and general weakness, which is particularly serious in that it often 
renders the body more susceptible to the attack of other diseases. 
Common malaria is rarely fatal, but it does weaken the body's 
resistance. . Tropical malaria is often fatal. 

Diagnosis. The presence of malarial parasites may be ascer- 
tained by a microscopic examination of a blood sample. Chills, 
followed by fever often come with other, diseases such as typhoid 
and appendicitis, which are sometimes diagnosed as malaria. A 
microscopic examination gives a conclusive test for malaria as the 
Plasmodia will be found' present in the suspect's blood. 

Treatment. Frequent doses of quinine bring about the de- 
struction of the malarial parasite, but because of the peculiar effect 

Photomicrograph of a mosquito's head. 

The female Anopheles is the carrier of the malarial germ. The male does 

not feed on human blood. 

of quinine on the nerves of the ears, and on the salivary glands, it 
must be used with care and discretion. 


Prevention. The control 
of malaria depends upon the 
destruction of malaria germs 
in patients by the use of qui- 
nine and the destruction of 
the mosquitoes (Anopheles). 
The frequent use of quinine 
in malarial regions by those 
not sick will kill the parasite 
before it has a chance to 
multiply. The rooms oc- 
cupied by malarial patients 
should be thoroughly 
screened, so that the disease 
may not be spread through 
the infection of more mos- 
quitoes. In fact, all dwell- 
ings in any malarial district 
should be well screened. Since the mosquitoes are in search 
of food in the evening, it is unwise for people to go beyond 
screen protection after dusk. Probably the best method of eradi- 
cating malaria is to destroy the breeding places of the mosquitoes 
by draining the swamps and filling in the low places. 

Photomicrograph of malarial parasites in a red 
blood corpuscle. 

Yellow Fever 

Prevalence of yellow fever. Yellow fever is a much more severe 
disease than malaria. The mortality in various epidemics has 
ranged from 15 per cent to 85 per cent of the population. It is 
also a disease which is more prevalent in tropical and subtropical 
countries than in cooler climates. Formerly, epidemics occurred 
in the Southern States, and the disease was very common in Cuba 
and the Canal Zone. Much has been accomplished in the last 
thirty years in eradicating this disease. In 1878, there were one 


hundred and twenty-five thousand cases and twelve deaths from 
yellow fever in the United States. Since 1905 not a single case 
has been reported. Havana and Rio de Janeiro used to b(Tcen- 
ters of infection. To-day, due to the control of yellow fever, they 
are health and vacation resorts. There is still one very bad dis- 
trict in western Africa. Efforts are now being made to control 
the fever there. 

History of the control of yellow fever. It is claimed that yellow 
fever was the disease that nearly annihilated the second expedi- 
tion of Columbus in Santo Domingo in 1495. 

Yellow fever was so bad in certain parts of Cuba that no one 
could live there safely. In 1900, after the Spanish-American 
War, a commission was appointed to make an investigation of 
yellow fever in Havana. The 
commission was composed of 
Major Walter Reed, a bacteriol- 
ogist, and Dr. James Carroll, 
Dr. Jesse W. Lazear, and Dr. 
Aristides Agramonte. Dr. Reed 
could not find a microorganism in 
the blood of the infected people. 
He decided that if the fever 
were caused by a bacterium, the 
nurses handling the patients 
would contract the disease. This 
did not seem to be true. He also 
observed that members of the 
same family did not seem to get 
the disease from each other. 
At the end of two or three 
weeks, people in the neighbor- 
hood of the original cases would 

Contract the disease. This Photomicrograph of a mosquito larva. 


seemed to indicate that the germ was transmitted by a carrier, 
possibly an insect, and it took that length of time to grow in the 

Am. Museum of Nat. Hist. 
The numerous swamps of Havana were the breeding places for mosquitoes, and yellow 
fever was very prevalent. By 1900, the effect of the extermination of mosquitoes began to be 
evident in a lower death rate of yellow fever. 

insect's body. Probably the knowledge of the cause of malaria 
gave these investigators clues on which they based these theories. 

People had formerly thought that yellow fever was transmitted 
by fomites, substances such as garments and bedding, which had 
been in contact with yellow fever patients and had absorbed the 
germs. To test the fomes theory, an experimental hut was 
filled with articles from a hospital for yellow fever, at Havana. 
Volunteers agreed to sleep in this hut. They did not contract 
the disease. The experiment was repeated with a number of 
persons and always with the same results, which definitely proved 
that fomites did not transmit the disease. 

The theory that the disease was transmitted by mosquitoes 


was then investigated. No animal was susceptible to yellow 
fever, so Major Reed could not experiment on animals. Dr. 
Carroll permitted himself to be bitten by a mosquito known as 
the Aedes or Stegomyia mosquito which was suspected of trans- 
mitting the fever. He contracted yellow fever but recovered. 
A mosquito accidentally alighted on Dr. Lazear's hand and he 
permitted it to bite him. He died September 25, 1900, one of 
the first martyrs to the yellow fever investigation. 

Major Reed then decided to set up controlled experiments to 
prove definitely whether or not the mosquito carried the disease. 
He wanted to segregate a group of men for a number of weeks 
from all contact with yellow fever to make sure they had not 
already contracted it before mosquitoes bit them. He asked fcr 






' Deaths in 
tt avarice 
from i 
TTakrria ] 













o 1 M Sfli&'v^lk 

1675 ifteoiees iseo i$9s two taos u»» 

Am. Museum of Nat. Hist. 
Due to the control of the mosquito, malaria has practically disappeared from Harana. 

volunteers for the experiment. Private Kissinger of Ohio and 
John J. Moran, a civilian clerk, offered themselves. Major Reed 

WH. FITZ. AD. BIO. — 32 


carefully explained the dangers of the experiment. The volun- 
teers said they understood the ravages of the disease but "we 
volunteer solely for the cause of humanity and in the interest of 
science." They'asked for no compensation for their services. It 
was a tense, dramatic moment when the Major raised his hand in 
salute to the private, saying, "Gentlemen, I salute you!" His 
further comment was, " In my opinion this exhibition of moral 
courage has never been surpassed in the annals of the army of the 
United States." Kissinger and Moran were bitten by mosquitoes. 
They both contracted yellow fever but both recovered. After 
studying many other cases, the investigators concluded that 
the only way to contract yellow fever is through the bite of an 
infected mosquito. It takes about twelve days for the parasite 
to complete its cycle in the mosquito's body. Therefore, an in- 
fected mosquito does not transmit the disease until about twelve 
days after 'taking in the -parasite from the body of an infected 
person. * 

Am. Museum o/Alat. Hist. 
Camp Lazear, Cuba, was the experimental camp in which the yellow fever investigation was 
conducted. It was named for Dr. Jesse W. Lazear, who died a martyr to the investigation. 

For 130 years Havana had been continuously infested with yel- 
low fever. The average death rate from it was about 750 deaths 


per year. After the yellow fever investigation, Major Gorgas 
was sent by the United States government to rid Havana of mos- 
quitoes. Within ninety 
days there was not a single 
new case of yellow fever. 

The Isthmus of Panama 
was considered a plague 
spot for yellow fever and 
malaria. About 1880, the 
French started building a 
canal across the Isthmus, 
but had to give it up, be- 
cause of the prevalence of 
the diseases which caused 
the death of thousands 
of the workers. Twenty 
years later, the United 
States bought the Isthmus 
from the French. Since 
Gorgas had helped to rid 
Havana of yellow fever, 
the government sent him 
to eradicate yellow fever 
from Panama. There were 
neither suitable drains nor water supply in the cities, so Gorgas 
had a system of drainage constructed, the streets paved to elimi- 
nate water-filled ruts, the water supply of the cities improved, and 
the windows and doors screened against mosquitoes. Pools were 
either drained or oiled. Endless care, thought, and time were 
devoted to this work. In about two years yellow fever was 
eradicated from the Isthmus and the building of the canal was 
made possible. This was as great a hygienic feat as the canal 
was an engineering feat. 

Courtesy Rockefeller Institute 
The structure isolated by Dr. Nogucbi which is 
believed to be the cause of yellow fever. In the photo, 
the spirochaete is magnified 3000 times. 


Later Investigations. Hideyo Noguchi of the Rockefeller Insti- 
tute isolated a microorganism, called a spirochaete, from yellow 
fever victims in South America, which has been, until recently, a 
focus for yellow fever. It is more like a protozoan than a bac- 
terium. He made a vaccine from this organism, which is admin- 
istered early in the disease and is very effective. The disease 
has been practically exterminated in the Western Hemisphere, 
due to his efforts. But experimental workers in Africa were 
unable to isolate the spirochaete from the blood of victims of 
yellow fever in that country. They were unable to inoculate 
monkeys and guinea pigs with the disease as Noguchi had done. 
Apparently, the germ causing yellow fever in Africa was differ- 
ent from that causing the disease in South America. Noguchi 
went to Africa to investigate the disease and he succeeded in 
inoculating one species of monkey with the disease. Unfortu- 
nately Noguchi became infected with yellow fever in Lagos, 
Nigeria, and died in the spring of 1928. After he contracted 
the fever, he insisted that samples of his own blood be inoculated 
into monkeys. His associates carried on his experiments with 
the cultures which he had started. It has not yet been decided 
whether there are one or two types of yellow fever. From data 
left by Noguchi, the Rockefeller Institute for Medical Research 
is inclined to believe that there are two distinct forms of the 
disease. Scientists are most anxious to clear up the infection 
in western Africa before the transcontinental railroad is opened. 
If the disease spreads to the East Coast, it may pass over into 
India and southern China, which are full of the Aedes mosquito. 

Cause. A spiral protozoan, spirochaete, was discovered in 
1918 by Noguchi and designated by him as the cause of yellow 
fever. Experiments are being performed, at the present time, to 
determine whether or not the spirochaete is really the specific or- 
ganism causing yellow fever. The vaccine prepared by Noguchi 
has not yet been accepted as a definite preventive. 


Questions and Suggestions 

1. Discuss the prevalence of malaria in the world. 

2. How did the disease receive its name ? 

3. Discuss the experiments of Major Ross. 

4. Discuss the cause and spread of malaria. 

5. Discuss the life history of the malarial parasite, including 
both the asexual and sexual phases. 

6. What effect has malaria on the body ? 

- 7. How is malaria diagnosed ; how is it prevented ? 

8. Discuss the prevalence of yellow fever. 

9. Discuss the investigation conducted by Major Reed. 

10. What biological and sociological effects did the investigation of 
yellow fever have on Havana ? 

11. Why is the building of the Panama Canal considered as great 
a hygienic as an engineering feat ? 

12. Discuss the contribution of Hideyo Noguchi to the eradication 
of yellow fever. 

13. Discuss the cause and the method of spread of yellow fever. 

14. Discuss the prevention of yellow fever. 

15. Which of Koch's postulates was Noguchi unable to carry out 
in his investigation of yellow fever ? 

16. Does the government give pensions or aid in any form to per- 
sons (or their dependents) who have risked their lives in scientific 
investigations ? 

Supplementary Readings^ 

De Kruif, P., Microbe Hunters (Harcourt, Brace & Co.). 
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.). 
Haggard, H. W., The Science of Health and Disease (Harper & Bros.). 
Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.). 







The scavengers of the body. 

Antitoxins neutralize toxins. 

How is the body protected against bacteria? Are the protections 
adequate? Under what conditions are the defenses inadequate? 

Diseases of the body may be due to glandular disturbances 
such as cretinism; inadequate diets, as rickets; constitutional 
tendencies or disturbances ; or to infections from microorganisms. 
Parasitic microorganisms exist in great numbers, but most of 
them are either kept out of the body or destroyed when they enter 
the body. There are comparatively few diseases caused by bac- 
teria when compared with the existing number of parasitic 

Behavior of bacteria in the body. Bacteria have different 
modes of attack and different ways of breaking through the de- 
fenses of the body. Some bacteria actually destroy tissue. For 
example, the tuberculosis bacillus devours various tissue cells, 
and thus destroys them. It is thought that certain parasitic bac- 
teria which cause boils and abscesses send out enzymes which 
dissolve the white blood cells so that they can be absorbed by 
the bacteria. The pus formed in boils and abscesses is dead white 
corpuscles. Other bacteria act on the body chiefly through the 
toxins or exotoxins they produce. These pass into the tissues 
surrounding the bacteria, get into the blood, and circulate through 



the body. For example, diphtheria toxins produce soreness in a 
throat on which the diphtheria bacilli are multiplying, and the 
blood carries the exotoxins around the body. The heart, kiciney, 
or some other remote organ may be affected. The tetanus bacilli 
develop their exotoxin at the place where they enter the body. 
This toxin then goes to the various tissues, especially the nerves. 

Bacterial poisons or endotoxins result from the breaking down 
or the disintegrating of certain bacteria. It is thought by some 
scientists that these endotoxins are never produced, as are the 
exotoxins, by the bacteria themselves, but are only set free during 
the breaking down of the bacterial body. The typhoid germs 
contain a very powerful endotoxin; tuberculosis, too, has a 
strong endotoxin. These are probably due to the breaking down 
of the proteins in the bacteria cell and the consequent formation 
of substances that are poisonous to the tissues. They are more 
correctly called poisonous split-proteins. There is still a fourth way 
in which bacteria are related to disease. Protein foods are some- 
times attacked by bacteria and are only partly digested or broken 
down to a group of products called ptomaines, some of which are 
injurious to the body. Ptomaines differ from toxins in that they 
are products of food decomposition, while the toxins are products 
of bacterial manufacture. The ptomaines are usually formed in 
foods under storage conditions in the shop or house, and not in the 
body. For example, if protein foods are not properly preserved, 
bacteria may attack them, causing disintegration. Partially dis- 
integrated fish, crabs, cheese, oysters, or milk often contain 
injurious ptomaines and, when eaten, will have a poisonous 
effect on the body. 

How bacteria enter the body. One of the common avenues of 
invasion for bacteria is the alimentary canal. Bacteria of typhoid 
fever and tuberculosis are frequently taken in with milk or other 
food through the mouth. Pencils, finger nails, and drinking cups 
are often responsible for an attack of diphtheria or scarlet fever. 



The respiratory tract furnishes a means for the entrance of germs. 
Spray or droplets of sputum sneezed or coughed out may be 
breathed in by other people. Germs of pneumonia, diphtheria, 
scarlet fever, and colds often enter the body in this way. 

Certain other organisms enter the body through wounds or 
skin abrasions. These skin openings may be of various kinds. 
Cuts, scratches, torn hangnails, and cracked skin are responsible 
for the entrance of dirt which may carry not only tetanus germs 
but, when present, ringworm (a parasitic mold), hookworms, or 
other pathogenic organisms. Insect bites form openings through 
which germs may be introduced. The bite of an Aedes mosquito 
may transmit yellow fever ; the Anopheles mosquito, malaria ; the 
rat flea, bubonic plague ; the body louse, typhus fever ; and the 
tsetse fly, African sleeping sickness. The bites of rabid dogs, 
cats, wolves, and other animals are responsible for hydrophobia. 
Some organisms enter the body through the eyes. If the eyes 
are rubbed with an infected hand or dried with an unclean 
towel, such diseases as trachoma and pink eye may possibly 

Safeguards of the body against disease. The best defense of the 
body is the strong natural resistance that accompanies good health. 
As long as rules of health are followed, the vitality is likely to be 
high. Even though bacteria then invade the body the natural 

An unbroken skin is a protection against invading bacteria. If the skin is pricked or other- 
wise broken, bacteria may enter and cause an infection. 

protective substances and cells tend to control them with success. , 
If resistance is low, due to insufficient air or sunlight, inadequate 


diet, lack of proper exercise or rest, the body cannot use its natu- 
ral protective agencies to the fullest extent, and invading bacteria 
gain a foothold in the body, multiply, and bring about a condition 
of disorder known as disease. 

As long as the skin is unbroken it forms an effective barrier 
against the entrance of germs. There is, however, some doubt 
whether a bacterium or a Protozoa can gain an entrance only 
through unbroken skin. A few parasites such as hookworms are 
known to penetrate unbroken skin and may cause a disease which 
undermines the vitality, and results in great lethargy and conse- 
quent inefficiency. Just as soon as skin is abraded or broken all 
kinds of parasites may enter. Broken skin should always be 
treated with antiseptics to inhibit the growth of any germs that 
attempt to enter. Some antiseptics have an additional value 
of promoting healing. 

The tears which constantly wash the eye will remove any 
bacteria and drain them into the nose, from which they may be 
removed. (If bacilli prodigiosus, bacteria that are pigmented red, 
be dropped in the eye, they will shortly disappear from the 
eye and appear in the nose.) The tears are slightly antiseptic 
in action so that they exert a chemical as well as a physical 

The mucous membrane in the nose, mouth, and throat catch 
the germs on its sticky surface and prevent them from traveling 
further into the body. This mucus is slightly antiseptic in action 
and is responsible for the destruction of some germs. When the 
membrane has caught germs in its secretion, an irritation is set 
up which stimulates sneezing, coughing, or blowing of the nose. 
Phagocytes probably destroy some of these bacteria. There are 
usually some bacteria found in the nose, throat, and mouth. 
As long as the resistance of the body is high and there is no 
break in the membrane, these germs do not attack the body. 
The body in good condition seems to acquire a certain immunity 



to the germs which it constantly harbors. Saliva as well as mu- 
cus is weakly antiseptic. Hairs grow on the lining of the nasal 
passages and act as a coarse filter which strains dust particles 
from inhaled air. This dust may then be expelled from the nose. 
There are specialized epithelial cells in the windpipe and bron- 
chial tubes with numerous cilia on their free surfaces, which 
wave and fan bacteria or very fine dust particles up and out. 
The foreign particles are then coughed out of the throat. 

The gastric juice in the stomach probably digests many bac- 
teria with the food. The acid of gastric juice sometimes destroys 
or inhibits the growth of many germs. Such bacteria then pass 
on through the canal with the food. The high acidity in a dog's 
stomach will kill bacteria that will cause intestinal infections in 
man. Tuberculosis, typhoid fever, and dysentery germs are not 
affected by the action of gastric juice and will pass into the small 
intestine. Bacteria of putrefaction are always abundant in the 
large intestine. If they are too active, intestinal disturbances 
result. Most bacteria can work only in an alkaline medium; 
therefore to control and inhibit their activity, efforts are made 
to introduce acids into the large intestine. The acids in most 
foods are absorbed or neutralized before they reach the large in- 

Stepping on a tack, rusty nail, or other sharp objects may set up an infection. Tetanus has 
been known to get into the body in this way and cause blood poisoning. 

testine. A certain bacillus, called the Lactobacillus bulgaricus, 
is one of the organisms causing the souring of milk. When this 


bacillus is taken into the body, it is thought to go into the large 
intestine, where it creates an acid medium. Some scientists think 
this aids the work of the bacteria of putrefaction and, conse- 
quently, clears up auto-intoxication. Recently another strain of 
bacteria that sours milk has been found that seems to be more 
effective. It is the Lactobacillus acidophilus. These bacteria will 
live longer in the intestine than do the Lactobacillus bulgaricus. 
There are a number of other conditions that protect the body 
against the invasion of germs. Even after germs enter, very 
few can cause a disease unless they multiply in great numbers. 
The body may be thought of as a great living culture medium. 
The inside is dark, moist, warm, and supplies food in the form of 
digested foods or tissue cells for invading saprophytes or parasites. 
In reality, each specific germ needs a definite combination of con- 
ditions. For example, the temperature of the body is not high 
enough for the bird type of tuberculosis. Therefore, this type 
cannot attack man. The human type grows only between 
37° C. and 40° to 41° C. A bird's temperature is much higher 
than man's, so that human tuberculosis cannot grow in birds. 
Bacteria that ordinarily attack warm-blooded animals are not 
likely to affect cold-blooded ones. If, however, the temperature of 
the cold-blooded animals is raised, they become susceptible to the 
invading germs. Frogs are naturally immune to tetanus, but if 
their temperature is raised, they become susceptible to the disease. 
Bacteria such as tetanus are anaerobic and grow only in the 
absence of air. If tetanus enters a surface wound exposed to 
air, it does not multiply. It is only when it enters deep wounds, 
where there is no air present, that it sets up an infection. Most 
tissue cells offer a high natural resistance to the entrance of germs. 
It is only when they are torn or lacerated that conditions are favor- 
able for the growth of germs in them. Many bacteria taken in with 
food are of the saprophytic type. They make no attempt to at- 
tack the tissues but simply feed on food in the alimentary canal. 


When bacteria actually enter the body and get into the blood 
or. lymph stream, there are many methods of protection. The 

Opsonic* InoleK '[Determination. 

Toactericc bacteria, 

+, -f 

fxxttents serum (control) normal serum. 

+ + 

"vhite corpuscles -nrhite corpuscles 

aq ^- percentage corpuscles <)* 
^*C ingesting bacteria — ►• ^^ 


— =2 patient's opsonic index 

Opsonins affect bacteria so that white corpuscles can more easily engulf them. Definite op- 
sonic indexes may be calculated from microscopic examinations. A pipette, marked as shown 
in the diagram, is used to measure the amounts of bacteria in the patient's serum and white 
corpuscles used in the test. 

white corpuscles devour bacteria and digest them. Thus, the body 
is rid of them. If numbers of bacteria get into the lymph system, 
they are frequently carried to a lymph node or gland, where the 
bacteria are filtered out. Then a collection of corpuscles attack 
the invading germs and destroy them. When a number of 
tuberculosis germs are combating white corpuscles in a lymph 
gland, the body sometimes deposits a wall of calcium around the 
infected center. This removes the whole mass of infected material 
from the circulation. Infected lymph glands are sometimes cut 
out of the body to prevent a possible reinfection from the tuber- 
culosis germs inclosed. 

The type of white corpuscle that devours bacteria is the 
phagocyte. When germs invade the body, there is an increase 
in the number of phagocytes produced in order to check the in- 
fection. If blood is examined, and the number of white cor- 
puscles is very great, this may indicate an infection in the body. 


Antibodies. There are many protective substances produced 
in the blood in response to the entrance of disease germs or their 
poisons. These substances are known as antibodies. Both 
toxins and. antibodies are specific for each disease. The toxin 
produced by a typhoid bacillus will cause only typhoid and will 
never cause diphtheria or any other disease, and the anti- 
toxin made by the body to fight diphtheria will have no effect 
on any other disease but diphtheria. This is true of all anti- 
bodies. Antitoxin is one type of antibody produced in the blood 
for the neutralizing of exotoxins. There may be antitoxins in 
the blood for diphtheria, others for scarlet fever, and still others 
for tetanus. The antitoxins neutralize the toxins produced by 
the bacteria and at the same time the phagocytes destroy the 
actual bacteria. 

Other protective bodies called lysins are present in normal 
blood, which actually dissolve the bacteria. The lysins which 
dissolve the bacteria are known as bacteriolysins. There are 
specific bacteriolysins produced to dissolve diphtheria germs. 
Others dissolve typhoid bacilli and still others dissolve meningitis 
germs. There are other kinds of lysins besides bacteriolysins. 
One kind may dissolve foreign red blood corpuscles and is called 
hemolysins. In blood transfusions, if one group of blood is intro- 
duced into another group of blood, the hemolysins of the first blood 
may dissolve the corpuscles of the second type. Therefore, trans- 
fusions are made only among bloods belonging to similar groups. 

Certain protective substances are produced in blood to assist 
the white corpuscles. For example, agglutinins cause the germs 
to stop moving and to gather in clusters or clumps. Then the 
phagocytes and lysins can destroy them more quickly. Agglu- 
tinins are produced in the body in combating typhoid. 

There are also precipitins known to the biologist. Their action 
is similar to that of agglutinins. They are specific for different types 
of foreign proteins, bacterial and otherwise. Precipitins harden 


or precipitate foreign proteins out of the blood. They are used 
as a test for specific bloods, human and other animals. 

Opsonins prepare the germs for ingestion by the white corpuscles. 
Opsonins seem to combine in some way with the bacteria and so 
alter them that the white corpuscles can better engulf them. 
There are different opsonins produced by the blood in combating 
tuberculosis, boils caused by a staphylococcus, and meningitis. 
When opsonins are present, the white corpuscles are better able 
to destroy the bacteria. The test for the amount of opsonins 
in a patient's blood is a very interesting one. For example, blood 
is taken from a patient suffering from tuberculosis, and the serum 
is separated from it. The amount of opsonins in this serum is to 
be measured. The serum is mixed with white corpuscles from a 
healthy animal or person. The white corpuscles are well washed 
to make sure that no opsonins are in the mixture before the 
serum is added. The serum and white corpuscles are then 
added to some tuberculosis bacilli. A little of this mixture is 
put on a glass slide, stained, and examined under the microscope. 
Then a count is taken, either of the number of bacteria ingested 
by the first hundred corpuscles seen, or an estimate of the per 
cent of the first hundred white corpuscles seen to have ingested 
bacteria. The second estimate is easier than the first because 
the white corpuscles devour so many bacteria that in some cases 
it is impossible to count them. The estimate is then compared 
to normal blood in order to see the increase of opsonins present, 
and thus determine the increase in the activity of the white cor- 
puscles. Any difference in the white corpuscle activity is attrib- 
uted to extra opsonins developed in the patient's blood. 

The relation of mental poise to disease. In his farewell address 
as the retiring dean of the college of physicians and surgeons of 
one of the large universities, a famous doctor stated that the sugar 
pill was the outstanding discovery of his generation. He stated 
in very decided terms that his long years of experience had con- 


vinced him that it was not so much the medicine as the fight 
that the patient made, which augmented and strengthened the 
defenses of the body. A sense of humor, joy, courage, optimism, 
and faith are true defenses against disease. A healthy and con- 
tented mind in a properly functioning and intelligently cared for 
body is the goal that each reader should strive to achieve. 

Questions, and Suggestions 

1. Discuss three ways in which bacteria attack the body. Illus- 
trate each with a specific disease. 

2. Discuss the different ways in which bacteria enter the body. 

3. Discuss the natural defenses of the body against the invasion of 

4. Discuss the protective substances found in the blood, which pre- 
vent the activity of the bacteria in the body. 

Supplementary Readings 

Broadhurst, J., How We Resist Disease (J. B. Lippincott & Co.). 
Greaves, J. E. & E. O., Elementary Bacteriology (W. B. Saunders Co.). 
Zinsser, Hans, A Textbook of Bacteriology (D. Appleton & Co.). 


Paul Ehrlich 

Eli Metchnikoff 

Why can some people resist disease successfully and others haw 
very little resistance? What theory of immunity is most generally 
accepted? Can all people be made immune to disease? 

The ability of the body to resist disease is known as immunity. 
To-day, when the emphasis is placed on preventive medicine rather 
than curative, immunity is one of the most important phases of 
biology. It is a comparatively new science. Two men largely 
responsible for founding the science of immunity were Eli Metchni- 
koff and Paul Ehrlich. 

Eli Metchnikoff. By 1883, Pasteur and Koch had succeeded 
in arousing in many scientists an interest in microbes. Metch- 
nikoff, a Russian naturalist working in Sicily, studied the way 
sponges and starfish digest their food. In investigating these 
animals he noticed certain cells moving in their bodies. These 
wandering cells acted and looked like amoebas. He fed par- 
ticles of powdered carmine to the transparent larvae of starfish 
and the wandering cells ingested the particles. Metchnikoff 
wondered whether these wandering cells would engulf microbes. 
He stuck some thorns from a rose bush into the transparent 
starfish. Masses of the wandering cells crowded around the 
slivers. He concluded that these cells killed invading germs, and 



he gave to them the name phagocytes. He published many 
articles and gave lectures concerning his discovery. 

Metchnikoff went to Paris to continue his work in Pasteur's 
laboratory, Pasteur believed in MetchnikofFs theory of phagocy- 
tosis, but Von Behring did not. The latter had already demon- 
strated that if tiny quantities of the poisons of tetanus and 
diphtheria were injected into rabbits, the rabbits became used to the 
toxins and did not become ill. Von Behring thought that chemical 
substances in the blood were responsible for this protection. This 
experiment was done before the germ of tetanus had actually been 
discovered. Von Behring felt certain that the plasma of the blood 
and not the phagocytes killed the germs and their poisons. 
We now know that both Von Behring and Metchnikoff were 
right. Not only do phagocytes devour germs, but blood pro- 
duces protective substances, lysins, that dissolve bacteria, and 
antitoxins that neutralize bacterial toxins. Metchnikoff formu- 
lated the phagocytosis theory of immunity, in which he stated that 
phagocytes alone were responsible for immunity. Later he agreed 
with Von Behring, that the blood contained other antibodies. 

Paul Ehrlich. A German medical student, Paul Ehrlich, was 
working on the staining of tissues. He believed that the reaction 
of certain bacteria to special drugs or stains might be a method 
of killing these bacteria without injuring the organism they were 
invading. If he could find stains or dyes with the ability to 
attach themselves to certain bacteria, he might introduce a poison 
with the dye and thus kill the dyed bacteria. In his staining 
experiments he had seen tuberculosis bacilli before Koch had, 
but had not recognized them nor described them as such. 
When Koch isolated the tuberculosis bacilli, Ehrlich showed 
him a simple method of staining them. Ehrlich inoculated 
mice with different dyes to see whether he could not make 
them immune to a certain disease caused by a spirochaete. In 
1893, after over six hundred attempts, he discovered an arsenic 

WH. FITZ. AD. BIO. — 33 



compound called 606, which gave immunity to the mice. Ehrlich 
tried his 606 on a certain disease in human beings caused by spi- 





r to*cin. 

ee ii 

£& in 

•totems on or 

Diagrammatic representation of toxins uniting with antitoxins. The toxin has stimulated the 
cell to develop an antitoxin which locks or neutralizes the toxin. This is according to the side- 
chain theory of Paul Ehrlich. 

rochaetes and found that it cured them, also. He called the arsenic 
compound salvarsan. He thought the salvarsan united with the 
cells of the body and helped to produce an immunity. Instead, it was 
later proved that the dye united with the spirochaete and killed it. 

Ehrlich was the founder of the humoral or side-chain theory of 
immunity, which is still generally accepted by biologists of to-day. 
The humoral theory states that protective substances are produced 
within the body, usually in the blood, which counteract the effects 
of bacteria. Metchnikoff and Ehrlich stimulated research in the 
study of immunity. Since then there has been much progress. 
To-day, it is one of the big features in preventive treatment. 
Many of the cures and discoveries of to-morrow will be built on 
the foundations laid by these men. 

Types of immunity. Natural immunity is the immunity one has 
at birth. It stays with the individual always and, therefore, there 


is no need of an inoculation, nor any danger of an attack of the dis- 
ease against which there is the immunity. That there is a natural 
immunity of species is shown by the innumerable diseases of animals 
to which humans are not susceptible. Similarly, animals con- 
tract very few of the human diseases. A natural immunity is, 
also, evidenced by various groups of the same species, although 
this is somewhat relative. The natives of South America and 
Africa are more immune to yellow fever than are the white peo- 
ple. Perhaps this is due to a weeding-out process during which 
the fittest has acquired an immunity while the unfit died. This 
does not always explain natural immunity, however. Measles is 
a mild disease with white people, but fatal to natives of certain 
South Sea islands. Jews are more immune to tuberculosis than 
Irish and English people. Eskimos, Indians, and Negroes are 
highly susceptible to tuberculosis. The North American Indian 
seems to be immune to scarlet fever. The colored people in the 
southern part of the United States seem to have a natural resist- 
ance to diphtheria. This type of natural immunity is often 
called racial immunity. Certain members of the same race show 
a natural immunity to disease while others do not. For example, 
some children seem naturally immune to diphtheria as seen in 
their reactions to the Schick test. Whether natural immunity 
is the result of natural selection, or whether it can be explained 
by environmental conditions, is still not decided. 

Acquired immunity differs from natural immunity in that it is 
developed during the lifetime of the individual. There are two 
types of acquired immunity, active and passive. Active acquired 
immunity is produced by the body itself as a result of having the 
germs or the toxins of a disease enter the body. There are three 
ways in which this may be accomplished. (1) By an actual attack 
of the disease. If this method produces immunity for any appre-. 
ciable length of time, it is likely to last for life. For example, once 
a person has had typhoid, smallpox, or diphtheria he is likely to 


develop an active immunity which lasts for life. (2) By 'vaccina- 
tion. The introduction of dead or attenuated (weakened) germs 
of the disease, in small doses, stimulates the body to produce its 
own antibodies. In vaccinating against typhoid and yellow fever, 
the dead organisms are used. In smallpox, germs weakened by 
passing them through a cow are used to make up the vaccine. 
This is known as animal passage. In rabies, the germs are 
attenuated by drying them. Germs may also be weakened by the 
application of slow heat or by growing them on media that are 
not quite favorable. In each of these cases the body cells respond 
to the inoculation by producing antibodies. (3) By the injection 
of toxin from which the bacteria have been filtered. Sometimes the 
toxin has some antitoxin mixed with it to dilute and make it 
safer, as in diphtheria toxin-antitoxin. Sometimes small quan- 
tities of the toxin itself are used, as in scarlet fever immunization. 
Here, again, the body produces antibodies. All actively acquired 
immunity is usually lasting in its effects. Active immunity takes 
some time to produce because the cells require time to make 
their reactions. 

Passive acquired immunity is obtained by the injection of anti- 
toxins or immune serums from the body of another person or an 
animal. Such immunity is immediate in its effects, but it does not 
last for very long. The antitoxin is already prepared. It sets to 
work promptly neutralizing the toxin present. The injection of 
such material does not stimulate the body to produce its own 
antibodies and hence this immunity lasts for only a short time. 
It is used in the actual treatment of the disease or to protect some 
one who has been exposed. For example, diphtheria patients and 
their families are given antitoxin. An immune serum is frequently 
given for pneumonia and infantile paralysis. 

The immunity of to-morrow. A very recent investigator, d'He- 
relle, has demonstrated the presence of what he has called a bac- 
teriophage, a kind of super bacteria that destroy other bacteria 


and produce an immunity. Experiments have been made in 
France and are now being conducted at Harvard and Yale uni- 
versities with this material. Watch for results of the work. The 
problem of immunity is still far from its solution. Scientists are 
just beginning to solve many of the questions. You who are to 
be scientists of to-morrow will have opportunity for research in 
this and many other fields of biology. 

Questions and Suggestions 

• 1. Discuss Metchnikoff's experiments with phagocytes. 

2. Give a report on the life and work of Metchnikoff. 

3. Discuss Ehrlich's experiments with dyes and chemicals on 

4. What theory of immunity was founded by Ehrlich ? 

5. Give some interesting facts about the life and work of Ehrlich. 

6. Discuss natural immunity ; acquired immunity. 

7. What test may be used to see whether a child is or is not 
naturally immune to a certain disease ? 

8. What specific inoculations should be given all children to make 
them actively immune to diseases with which they come in contact? 

9. What specific inoculations should be given a person who is 
traveling to make him actively immune to diseases with which he 
might come in contact? 

10. State two differences between active and passive immunity. 

11. Under what conditions will a person be actively and passively 
immunized against diphtheria ? 

12. Answer some objections that may be currently raised against 







"Mammalia ■ 







[ Species Somestica 

' iTj&ivi&ual "from. 


A cat named Tom 

How can the many plants and animals of the world be identified f 
What is the purpose of identification? What is taxonomy? What 
contributions made by scientists have helped to systematize the classi- 
fications of plants and animals ? 

It is said that Alexander the Great was a pupil of Aristotle, the 
Father of Biology. Alexander held his teacher in the highest 
esteem, and, during his campaign and conquests, kept a group of 
couriers to carry unusual plant and animal forms back to his friend 
and teacher. These specimens came in such large numbers that 
Aristotle had to devise a means of caring for them in an orderly 
manner. He used a system of classification that was largely based 
on the habitat of the organisms. For his animals he had eight 
groups, four of which were blood-containing, and known as mam- 
mals, birds, egg-laying quadrupeds, and fishes; while four were 
bloodless, namely, squid-like animals, Crustacea, insects, and 
animals with shells. 

The binomial system of Linnaeus. Various other scientists 
changed this system, but Carolus Linnaeus, a Swedish natu- 
ralist, devised the system upon which the modern method of 
classification is based. Before his time, in order to describe a 
kind of grass and not confuse it with other forms more or less 



like it, a descriptive name similar to the following was used : Gramen 
Xerampelino, Miliacea, praetenius ramosaque sparsa panicula, siya 
Xerampelino cogener, arvense, aestivum. Carolus Linnaeus^ was 
an assistant to the Professor of Botany in the University of 
Upsala, Sweden. While cataloguing plants, he had come across 
many descriptions such as the one just given. He realized that 
such a name was too long and inconvenient and he initiated a num- 
ber of reforms in the existing scheme of classification. He gave 
the name " Pea bulbosa " to this plant. In his system which he 
called the binomial nomenclature, two names sufficed to dis- 
tinguish this organism from all others. One .name designates 
the genus of the plant or animal, the other the species. All 
organisms that have similar characters are grouped together and 
this group is called a genus. The' name given them is the generic 
name. The genus is subdivided into groups with varying char- 
acters called a species and the name given is the specific name. 
The generic name for all the members of the cat tribe is Felis. The 
genus Felis is subdivided into the species such as leo (lion), par- 
dus (leopard), domestica (house cat). Therefore, the lion is 
known as Felis leo, the leopard as Felis pardus, and the house 
cat as Felis domestica. The initial letters of the name of the 
genus is always capitalized and that of the specific name is written 
with a small letter. 

What a task Linnaeus undertook ! He published his most impor- 
tant work, Systema Naturae, in twelve editions and like all scien- 
tists of his time, wrote the descriptions in Latin. This practice 
continued until very recently. Exchanges of scientific papers on 
classifications could be made throughout the world in a common 
language. Recently, scientists have employed their mother tongue 
for the description of any new creature. When the discovery is an 
important one, the paper is translated by those who need the data. 
Linnaeus died in 1778, but his work lives on and, with a few modi- 
fications, is still used to-day. 


N. Y. ZoSlogical Society 
There are marked differences in size, shape, and habits of present day mammals. The 
giant anteater, Myrmecophaga jubata, is a native of tropical America. Its coarse hair is almost 
bristle-like in structure. The long narrow snout and a long tongue enable it to lick up in- 

The basis of the classification of to-day. The scientist of to-day 
knows many more animals than Aristotle or Linnaeus knew. 
There are probably more than a million different kinds of ani- 
mals now known, and nearly as many plants. With the method of 
identifying and classifying animals and plants in an orderly and 
scientific manner there has grown a division of biology, taxonomy, 
that is concerned with this classification. Taxonomy (from taxis 
— arrangement; nomos — law) is the division of biology that 
has to do with the classification of animals and plants on the basis 
of fundamental similarities. The modern method of classifica- 
tion of plants and animals does more than catalog animals for 
the convenience of the scientists. It expresses a kinship and rela- 
tionship. The relationship of plants and animals has been de- 

'the basis of the classification of to-day 513 

termined from their structure, embryology, habits', habitat, ability to 
crossbreed with related forms, and from certain other facts. 

By structure is meant the shape and arrangement of the parts of a 
plant or animal. Certain plants are grouped together because they 
have chlorophyll ; certain animals are classified together because 
they have six legs. The embryology of a plant or animal refers to 
its development from the time it is first formed until it is a full- 
grown adult. A caterpillar looks somewhat like a worm which is 
really one of the stages in the life history of an insect. Plants and 
animals that have similar embryological developments are closely 
related; those with dissimilar embryological developments are 
not closely related. Animals and plants which are closely related 
usually have some similar habits. In general, most water plants 

N. Y. Zoological Society 
The duckbill (Ornithorhynchus anatinus) is an egg-laying mammal, native of Australia. It is 
covered with dark fur, and has a bill and five-toed webbed feet. 



are closely related. Animals that carry their young in pouches are 
classified together. Birds that have wading habits belong to the 

N. Y. Zoological Society 
The Armadillo (Tatu novencinctum) is covered with a bony shell. Some species can curl up 
into a ball, presenting the armor on all sides. 

same group. Habits alone do not determine classification ; other 
facts must be considered. The whale is frequently thought of as 
a fish because it swims and lives in the water. Actually it is a 
mammal because it suckles its young. When animals or plants 
crossbreed with each other, they are usually found to be closely 
related. For this reason successful crossbreeding is only possible 
with those forms that are closely related. For example, the 
horse and donkey will crossbreed and produce a mule. The mule 
is probably always sterile, and will not produce offspring. Dogs 
and wolves will crossbreed and the hybrid offspring will repro- 
duce. Consequently, dogs and wolves are thought to be more 
closely related than are horses and donkeys. 

The Law of Priority. So many modifications of Linnaeus' sys- 
tem of classification arose that confusion resulted. An Interna- 
tional Commission on Classification was founded in 1895. Its pur- 
pose was to draw up a set of rules which would be accepted and 



adopted by the scientists of the entire world. One of the basic 
rules formulated by this commission is the Law of Priority. This 
has to do with the scientific name each animal and plant^is to 
bear. Suppose an unfamiliar microscopic animal is observed. The 
scientist draws it, photographs it, perhaps he kills it, and studies 
it as stained and sectioned material. He then consults the de- 
scriptive classification organized since 1895 and seeks the proper 
place to catalog his specimen. If the specimen is not similar to 
any known organism, the scientist gives it a generic and specific 
name, writes a description, and publishes his findings. If no 
other scientist reading his paper has ever come across it or seen 
a description of it elsewhere, this scientist is thereafter credited 
with the discovery. He has added a new creature to the list of 
known organisms. 


*Kyriccpoola Onychoptaonec 

rjtxcny-va^i*^ Ws -me surviving 

brings present 

ensfflang legk aquatic, artTit-oTDOct^ 



The phylum Arthropoda is subdivided into five present-day classes. There are many fossil 
arthropods, some of which are quite unlike present-day forms. 

The method of the classification of to-day. All living things are 
placed into one of two kingdoms, the plant kingdom or the ani- 



mal kingdom. These two kingdoms are further divided. Cer- 
tain outstanding likenesses enable a scientist to divide the plant 

Museum of Natural History 
The Crustacea vary in size and shape from microscopic representatives to lobsters weighing 

nearly fifty pounds. 

kingdom into four divisions called phyla (singular, phylum). In 
this book the animal kingdom will be divided into ten phyla. 
The various phyla have been carefully analyzed and compared, 
and finer groupings, called classes, made. Again a finer sorting 
is made and the classes are split into orders. Certain char- 
acters again permit a subdivision of the orders into genera. The 
genera are separated into groups showing very close relationship. 
These are the species. They are very much alike, but may still 
differ slightly in form, habitat, or distribution. 

One phylum of animals, the arthropoda, is distinguished from 
the other ten phyla in that all of its members are segmented, 
have an exoskeleton and jointed legs. One of the classes of the 
phylum arthropoda has a characteristic exoskeleton impregnated 


with lime. The organisms with a lime skeleton are put in the class 
called the Crustacea. All the arthropods with' lime skeletons and 
ten legs are then grouped into an order, the Decapoda. In this 
order are found the crabs, lobsters, crayfishes, and the like. The 
different members of the order Decapoda are then separated into 
various genera and species. The sea-living lobster belongs to the 
genus Homarus, while the land-living and fresh-water crayfish 
belongs to another genus, Cambarus. There are different species 
of lobsters in the genus Homarus. The North American lobster 
belongs to the species americanus which is slightly different from 
the European lobster, vulgaris. The farther down the scale of 
classification the closer is the relationship. Species are more 
closely related than genera and, in turn, genera are more closely 
related than orders, etc. 
Phylum Arthropoda. 
Class Crustacea. 
Order Decapoda. 
Genus Homarus. 
Species americanus (American Lobster). 
The Paramecium may be similarly classified. 
Phylum Protozoa (one-celled animal). 

Class Infusoria (numerous hairlike processes used for loco- 
motion and feeding, presence of fixed openings for 
food ingestion and the extrusion of solid wastes). 
Order Holotrichia — animals with cilia of equal length dis^ 
tributed over the entire body. 
Genus Paramecium. 
Species caudautum. 
Using this modified Linnaeus method, let us consider a butter- 
cup. It belongs to the great branch of phylum of the plant king- 
dom known as the Spermatophyta. It is placed in the class Angio- 
spermae. It is of the genus Ranunculus, and there are many 


The classification of man is another example. 

Phylum Chordata (most members have backbones and have 
central nerve cords). 
Class Mammalia (presence of hair ; the young are fed on 
milk ; a muscular diaphragm separates the thorax from 
the abdomen). 
Order Primates (erect or nearly so). 
Genus Homo. 
Species sapiens. 

Classification of plants. 



The plant kingdom is divided 
into four large groups called 
phyla. The flowering group 
of spermatophytes are the most 
recent plants. 

I. Phylum THALLOPHYTA (thallus — young branch ; phyton 
— plants). Includes very simple plants, sometimes single-celled, 
but more often many-celled; some have chlorophyll, others are 
without this green material ; none have roots, stems, or leaves. 

There are two subphyla, Fungi and Algae. The Fungi are 
non-green plants of very great economical importance. There 
are four classes found in the subphylum fungi. 
Class I — Fission fungi. Bacteria. 
Class II — Tube fungi. Have tubular bodies. Example is 

bread mold. 


Class III — Sac fungi. Produce spores in a sac. Examples 
are the yeasts, powdery mildews, and many others. 

Class IV — Club fungi are so-called because their spores are 
produced upon a club-shaped structure. Mushrooms, puffballs, 
smuts, and rusts belong to this group. 

The subphylum Algae includes the chlorophyll-bearing thallo- 
phytes. In some forms the chlorophyll is masked by some other 
coloring matter. They range from single-celled forms to filamen- 
tous colonies or even long ribbon or rope-like masses many feet in 
length. They are nearly all aquatic. The subphylum Algae is 
subdivided as follows : 

Class I — Blue-green algae contain a blue pigment in the 
cells in addition to the green color. Examples are Nostoc pru- 
niforme and Oscillatori violacea. 

Class II — Green algae are of countless forms, unicellular, 
filamentous, platelike, and in irregular masses of cells. There 
are both fresh-water and salt-water forms, and others live on 
land. One form will grow on snow patches. Pleurococcus vul- 
garis and Vaucheria terrestris are examples. 

Class III — Brown algae are nearly all marine plants. 
They are the commonly known seaweeds. 

Class. IV — Red algae are mostly marine. Our most deli- 
cate and beautiful seaweeds belong to this main class. 

II. Phylum — BRYOPHYTA (Gr., bryon — moss; phyton — 
plant) . Contains only two classes, the liverworts and the mosses. 
These plants are small and live mostly on land. They show a 
greater development of tissues than the algae and may be 
either thallus-like (liverworts) or have stems with rootlike pro- 
jections and very simple leaves. They reproduce by forming 

III. Phylum — PTERIDOPHYTA (Gr., pteris — fern). This 
includes a group which, when the world was younger, played a 
very important part in the vegetation on the earth. Most coal is 


made from ferns of the past. They have true roots, stems, and 
leaves, but reproduce like the mosses, by forming spores. The 
Pteridophyta include three classes : the true ferns, the horsetails 
(Equisetum), and the lycopods or club mosses. 

IV. Phylum— SPERMATOPHYTA (Gr., sperma— seed). The 
seed-bearing plants are grouped into two subphyla. The Gym- 
nospermae (Gr., gymnos — naked), or naked-seeded plants, 
include a small group related to the ferns on one side and the 
flowering plants on the other. Two classes are found in this sub- 
phylum: the Cycads, of which the so-called sago palm is an 
example, and the Conifers or evergreens, as pines, spruces, firs, 
hemlocks, cypress, and others. The evergreens include the 
sequoias, the largest and oldest trees. The subphylum Angio- 
spermae (Gr., angeion — case or vessel), or true flowering plants, 
include the common grasses and grains, flowering trees and shrubs, 
and flowering plants. It is divided into two sub-classes, Mono- 
cotyledones and Dicotyledones. 

The classification of animals. 

60.0 00 070rddCtc£Vp or .i A,r-cc 

v species / A? JsFTjZw 

-isooo^^l AnneliSLoc 

The number of species given 
in the diagram is approximate 
and not exact. 

Phylum I —r PROTOZOA (Gr., protos — first ; zoon — animal) . 
Single-celled animals without true organs, or tissues. Occasionally 


protozoa are colonial, in which case the unit cells of the colony 
are all potentially alike. There are four classes of protozoa. 

Class I — Rhizopoda (root-footed) . These cells have no fixed 
form. The Amoeba proteus is one of the best known animals in 
this class. The Amoeba histolitica causes a disease of the mouth. 
Amoeba dysentericus causes summer complaint in children. 

Class II — Mastigophora. Move by one or more long, whip- 
like threads of cytoplasm called flagella. Euglena viridis is an 

Class III — Sporozoa. Parasitic Protozoa, usually lacking 
motile organs or mouth. They reproduce by spores. Example : 
Plasmodium malariae. 

Class IV — Infusoria. Animals which have many vibratile 
processes (cilia), a cuticle, and fixed mouths and anal spots. 
Paramecium caudatum, Vorticella. 

Phylum II — PORIFERA (Lat., porus — pore; ferre — bear). 
Many-celled animals, so arranged as to form two layers of cells. 
Their bodies are usually penetrated by numerous pores. The 
cells of the body are supported by a skeleton of " spicules " or 
material called spongii." There are three classes. 

Class I — Calcarea. Sponges with spicules composed of cal- 
cium carbonate. Example : Grantia. 

Class II — Hexactinellida. Sponges with spicules of silica 
triaxon in form. Glass sponges. Venus flower basket. 

Class III — Demospongia. Sponges with skeletons of spicules 
of spongin or a combination of spongin and silicon. The bath 
sponge is an example. 

Phylum III — COELENTERATA (Gr . koilus — hollow ; enteron 
— intestine) . Composed of animals made of two layers of cells 
invaginated to form a gastrula or internal cavity; they have a 
mouth surrounded by tentacles and no anus. They are pro- 
tected by stinging cells which also aid in killing prey. 

Class I — Hydrozoa. Single animals like Hydra fusca or colo- 

WH. FITZ. AD. BIO. — 34 


nial animals, as Obelia weismania. These animals reproduce by 
buds, and by eggs and sperms. In the colonial types, certain 
buds of the original colony are free-swimming jellyfish. These 
produce the eggs and sperms. 

Class II — Scyphozoa. Marine jellyfish, large in size. Ex- 
amples are Aurelia flavidula and Portuguese man-of-war. 

Class III — Anthozoa. Large hydra-like animals, single or 
colonial, usually attached, with many tentacles arranged in 
circles of multiples of five. The sea anemones and corals are 
the best known examples. 

Phylum IV — PLATYHELMINTHES (Gr., platys — flat ; hel- 
minthos — worm), or flatworms. Three-layered animals, bilat- 
erally symmetrical, usually small, ribbon- or leaf-like, flat, and 
live in water. Most flatworms are parasitic. Examples are 
tapeworm and liver fluke. 

Phylum V — NEMATHELMINTHES (Gr., nematos — a 
thread), or round worms. Three-layered, elongated, thread-like 
animals, often parasitic. Vinegar eels, the horsehair worm, the pork 
worm or trichina, the threadworm, and the hookworm are examples. 
Phylum VI— ECHINODERMATA (Gr., echinos — hedge hog; 
derma — skin). Radially symmetrical, spiny-skinned animals 
which live in salt water, more complicated in structure than the 
worms. Five classes : 

Class I — Asteroidea. Starfishes. 

Class II — Ophiuroidea. The brittle stars or snake stars. 
Class III — Echinoidea. Sea urchins. 
Class IV — Holothuroidea. Includes the sea cucumbers. 
Class V — Crinoidea. Stone-like, deep-sea forms, now almost 
extinct. Sea lilies and sea feathers are examples. 
Phylum VII — ANNELIDA (Lat., anellus — a ring) . Bilateral, 
segmented worms; composed of body rings or segments. The 
digestive tract is a tube within a tubelike body. No jointed 
appendages. There are two classes : 



Class I — Archiannelida. Primitive marine worms without 
parapodia or setae. Example: Polygordiusr 

Class II — Chaetopoda. Bristles along the body. Examples 
are the earthworm or sandworm. 

Class III — Hirudinea. Without bristles and having suckers 
at both ends of the body. Examples are the leeches. 
Phylum VIII. MOLLUSCA (Lat., mollis — soft). Soft-bodied 
unsegmented animals, often provided with a shell which is secreted 
by a part of the body. 

Class I — Gastropoda (bellvrfooted). With or without shells, 
which, when present, are of one piece and coiled. Snails, whelks, 
and slugs. 

Class II — Pelecypoda (hatchet-footed). Shells in two 
valves or parts. Clams, oysters, scallops, and mussels. 

Class III — Cephalopoda (head-footed). Foot partly sur- 
rounds head and bears tentacles or grasping organs. Squids, 
octopuses, and cuttlefishes. 

Phylum IX — ARTHROPOD A (Gr., arthros — joint; pous — 
foot). Animals are segmented, and have chitinous exoskeletons 
and jointed appendages. They live in water, on land, in the air, 

The reptiles are legless vertebrates with a skin covering made of scale-like plates. 


or in all three places. Most of them undergo a metamorphosis. 
There are five classes : 

Class I — Onychophora. Primitive air-breathing arthropods 
with tracheae and nephridia. Peripatus capensia. 

Class II — Crustacea. Breathe by means of gills. The head 
and thorax are fused ; two pairs of antennae. They have a 
" crusty " exoskeleton, strengthened with lime. Examples, 
crabs and lobsters. 

Class III — Myriapoda (numberless legs). Have long bodies 
with many segments and many paired jointed appendages ; 
breathe by tracheae., Centipedes and millipeds are examples. 

Class IV — Arachnida (Gr., arachne — spider). This group 
has no antennae, four pairs of legs, and a pair of clawlike 
appendages on each side of the mouth. Head and thorax com- 
bined as in Crustacea. - Breathe by book-gills, book-lungs, or 
tracheae. The spiders, daddy-long-legs, scorpions, mites, and 
ticks are in this class. 

Class V — Insecta. The largest class of animals. Body seg- 
mented ; three body regions, head, thorax, and abdomen ; 
three pairs of jointed legs; usually compound eyes; breathe 
through tracheae or air tubes. Insects. 

Phylum X. — CHORDATA (Lat., chorda — cord). Animals 
having a skeletal axis, gill slits in embryo or adult, and a nerve 
cord dorsal to the alimentary canal. This phylum is divided into 
four subphyla, one of which is the Vertebrata in which a nerve 
cord is protected by a segmented, bony spinal column. These 
vertebrates are divided into seven classes. 

Class I — Cyclostomata. Eel-like vertebrates with round 
mouths and without functional jaws, without scales and fins. 
Lampreys and hagfishes. 

Class II — Elasmobranchii. Fishlike vertebrates without a 
bladder, with jaws, and with a cartilaginous skeleton. Sharks, 
rays, and skates. 



The relationships of the backboned animals is often shown by a tree. Animals supposed to 
have appeared early are on lower branches. The very recent animals and man are on the tips 
of the higher branches. Related animals are found on the same or nearby branches. ^ 

Class III — Pisces. The fishes. Aquatic, cold-blooded verte- 
brates breathing by means of gills, having an air bladder, a 
two-chambered heart, and a skinlike exoskeleton of scales. 

Class IV — Amphibia. Cold-blooded vertebrates breathing 
by means of gills in some stage of their life history. Skin is 
not covered with scales, the heart is three-chambered. Most 



amphibians undergo a complete metamorphosis. The larvae form 
comes from the egg and live in the water and possess gills. Frogs. 
Class V — Reptilia. Cold-blooded vertebrates usually cov- 
ered with scales, breathing throughout life by means of lungs. 
The heart is three-chambered. Lizards, snakes, and turtles. 

Class VI — Aves. The birds. Warm-blooded vertebrates cov- 
ered with feathers. Front limbs are wings ; they have air spaces 
in the bones, no diaphragm, and a four-chambered heart. Birds 
lay eggs with a shell of lime, and usually care for their young. 
Class VII — Mammalia. Warm-blooded animals covered 
with hair, at some stage. Usually have mammary glands and 
suckle the young. They have a diaphragm between the thorax 
and abdomen. This class may be divided into eleven orders : 
Order 1 — monotremata. Egg-laying mammals. Duck- 
bill, spiny anteater. 

Order 2 — marsupialia. Carry immature young in a 
special abdominal pouch. Kangaroo, wombat, opossum. 

N. Y. Zodlogical Society 
Darwin did not say that man came from monkeys. He and other evolutionists believe that 
there is a common ancestor 'of man and certain of the apes. 

Order 3 — Edentata. Toothless or with very simple teeth. 
Hairy anteater, sloth, armadillo. 


Order 4 — cetacea. Adapted to marine life. Whale, por- 
poise, dolphins. 

Order 5 — sirenia. Fishlike in form ; pectoral "limbs 
paddle-like. Examples : manatee, dugong, sea cow. 

Order 6 — rodentia. Incisor teeth chisel-shaped, usually 
two above and two below. Examples: beaver, rat, porcu- 
pine, rabbit, squirrel. 

Order 7 — ungulata. Hopfs ; teeth adapted for grinding. 

a. Odd-toe. Horses, zebras, rhinoceros. 

b. Even-toe. Ox, sheep, antelope, camel, giraffe, deer, 

pig, hippopotamus. 

c. Proboscidea. Elephants. 

Order 8 — insectivora. Small, insect-eating, furry or 
spiny covered ; long snout. Moles, shrews, hedgehog. 

Order 9 — chiroptera. Fore limbs adapted to flight, 
teeth pointed. Example : bat. 

Order 10 — carnivora. Long canine teeth, sharp and 
long claws. Examples : dog, cat, lion, bear, seal, and sea lion. 

Order 11 — primates. This order of animals includes man. 
Erect or nearly so, fore appendages provided with a hand. 
Lemurs, monkeys, baboons, mandrills, apes, gibbons, orang- 
utans, chimpanzees, gorillas are in this group. 

a. Lemuroidea. Small squirrel-like animals living in trees 

and bushes. The lemurs and marmosets. 

b. Cebidae. The New World monkeys. Grasping tails and 

flat noses. Howling monkey, spider monkey, capuchin. 

c. Cercopithecidae. The Old World monkey. Tail not 

grasping, or short ; nostrils pointing downward. Dis- 
tinct, opposable thumb. Baboon, mandrill. 

d. Simiidae. The anthropoid (man-like) apes. No dis- 

tinct tail; arms longer than legs. Gibbon, orang- 
utan, chimpanzee, and gorilla. 

e. Hominidae. The human race. 



Mixed cultures. Ordinary clear pond water may be used. Water 
take^n from an aquarium, in which plants have been growing, fre- 
quently contain Protozoa. If tap water is to be used, let it stand in 
open vessels for at least a week in order to let the chlorine or other 
antiseptic gases escape. 

Cultivation of Paramecia. Prepare a hay infusion by cutting 
timothy hay stems into short lengths. Fill a six-inch by eight-inch 
sterilized battery jar one half to two thirds full of water and add a 
small handful of the cut hay stems. Set the jar on a table in medium 
light and do not cover. After a few days a scum will form on the 
surface of the water. First bacteria and then Protozoa including 
Paramecia, will appear. The Protozoa will feed on the bacteria. A 
succession of forms will appear within a space of three to four weeks. 

Pure culture of Paramecia., Cut timothy hay stems into short 
lengths. Boil these with plenty of distilled water until the water turns 
brown. Three different concentrations of culture media should be 
prepared. Sterilize all glassware by boiling. 

Solution 1 — Put two heaping tablespoonfuls of boiled hay in a 
large beaker containing two thirds of the undiluted hay water. 

Solution 2 — Put one tablespoonful of boiled hay in a large beaker 
containing diluted hay water (half hay water, half boiled water, 

Solution 3 — Put a heaping teaspoonful of boiled hay in a large 
beaker containing two thirds of diluted hay water. 

Let the solutions ripen, exposed to the air for about a week. Then 
inoculate with a pure culture of Paramecia. 1 Check your solutions 
carefully so that you will know which one gives the best results. 

Cultivation of amoeba. Water weed method. — Boil some fresh 
water plants, Elodea or Ceratophyllum. Place a very few of these 



dead, though still green, water plants in the bottom of a 4 by 6-inch 
battery jar which has been carefully sterilized, and pour on aerated 
distilled water to a depth of 2\ to 3 inches. It is very important not 
to use too much plant material. In general, sufficient weed material 
should be added to cover the bottom with a greenish layer. In addi- 
tion, place in each culture 8 or 10 wheat grains which have been thor- 
oughly boiled. After the culture has stood for one week, add a pure 
culture of amoebas. If you have no amoebas, look for them in their 
natural habitat, e.g., pond or aquarium. Only a very small variety 
of amoebas are usually found in such places. If a greater variety is 
preferred, they may be purchased from a biological supply house. 1 
By re-culturing from time to time amoebas can be kept for the entire 
school year. 

The amoeba culture should be kept in medium light and in a cool 
room where the temperature does not vary greatly. An optimum 
of 20° C. (68° F.) is satisfactory. It is difficult to keep amoeba cultures 
during the summer because of the high temperature. However, if 
the cultures are stored in a cool, fairly well-lighted basement, the 
animals will usually survive. 

Upon the bottom of the properly prepared amoeba culture, there 
forms a greenish layer of loose material. Microscopic examination 
will show that this layer is rich in diatoms, desmids, and other plant 
cells and it is on and in this bottom layer of greenish material that the 
amoebas feed and multiply. Within a week or, at most, two weeks 
after inoculation the culture should be rich in amoebas which will 
generally live and reproduce for some time. 

The main point to be emphasized in connection with this type of 
culture is that the water must remain clear. That is, it should not 
become cloudy or show evidence of fermentation in the formation of a 
surface film or scum. If the culture develops either of these charac- 
teristics, too much plant material is present and such a culture should 
be thrown out and a new one started. 

1 Satisfactory cultures of Paramecia and amoebas may be obtained either 
from the New York Biological Supply House or J. D. Dawson, College of 
the City of New York, New York. 



Fuel Value of Certain Foods 1 

Name of Food 

Milk and Milk Products: 
Milk, whole .... 
Butter milk .... 
Cheese, American . . 
Cheese, cottage . . 
Cream, thin .... 


Ice cream .... 


Olive oil 

Cottonseed oil . . 

Bread and Cereals: 
Bread, white . . . 

Graham Bread . . . 

Boston brown bread 

Bran, wheat . . . 
Corn meal, cooked 
Hominy grits, cooked 
Macaroni, cooked . 
Oatmeal, cooked . 
Rice, brown, steamed 
Rice, white, steamed 


Egg, whole . . 

Egg, white . . . 

Egg, yolk . . . 

Meat, Fish and Poultry: 
Bacon, cooked . . 



1 in. cube 
3* T. 

pat, 1 T. 
I cup 


1 slice 
3 X3i 
X 1 in. 
1 slice 
3i X2 
Xf in. 
\ in. slice 
3 in. diam. 
J cup 
f cup 
i cup 
h cup 
f cup 
I cup 
f cup 

1 egg 
1 egg 
1 egg 

4-5 small 









. 88 














, 1 





























































1 Adapted from Charts in Amer. Red Cross pamphlet, "Food. Why? 
What? How?" 



Fuel Value of Foods (Continued) 

Name of Food 






Meat, Fish, and Poultry — 


Beef, lean, broiled 

2 slices, 






X H in. 

Chicken, roast .... 

1 slice, 
X i in. 




Fish, lean, broiled . . . 

1 slice, 
X 1 in. 




Ham, boiled 

1 slice, 
4f X6 





Lamb, chop, broiled . . 

1 chop 





Lamb, roast 

1 slice, 




" — 



Liver, calf, broiled . . 







Mutton, roast .... 

1 slice, 
Xi in. 




Oysters, raw .... 






Pork chop, lean, broiled 

1 chop 





Veal leg, lean, broiled 

1 serving 








4 stalks 
4 in. long 



» 1 


Beans, lima, dried . . 

i cup 

200 ' 


v 8 


Beans, lima, fresh . . . 

h cup 





Beans, dried 

i cup 





Beans, string, fresh . . 

| cup 






i cup 
in cubes 





Cabbage, chopped . . . 

i cup 







Name of Food 






Vegetables — Continued 

Carrots, cooked . . . 

2 medium 






l\ small 











— . 


Corn, fresh 

1 ear, 6 in. 





Corn, canned .... 

1 cup 






f cucum- 





Dandelion greens . . . 

§ cup 





Lentils, dried .... 

3f T. 






J head 






5 to 6 pods 






3 to 4 






i cup 
in slices 





1 cup 





Peas, fresh 

I cup 





Potatoes, white, boiled 

1 medium 





15 min. 

Potatoes, sweet, baked . 

1 medium 





Rutabaga, raw .... 

f cup 





Spinach, cooked . . . 

f cup 





Squash, cooked, summer 

i cup 





Tomatoes, fresh . . . 

1 small 





Turnips, cubes, raw . . 

i cup 





Fruits, Fresh: 

Blackberries .... 

i cup 





Cantaloupe . . 

| melon 





• Cherries, stoned 






Cranberries . . 

i cup 





Grape fruit . . 

h large 





Grapes, white . 






Huckleberries . 

i cup 





Lemon juice . . 






Olives, green 

4 medium 



. . 41 


Oranges . . . 

1 medium 







Fuel Value of Foods (Continued) 

Name of Food 

Fruits, Fresh — Continued 
Orange juice . . . 

Peaches , 


Pineapple .... 

Plums .... 
Raspberries . . 
Rhubarb . . . 

Fruits, Dried: 
Apricots . . . 
Dates, unstoned 
Figs . . . . 
Prunes . . . 
Raisins . . . 



Pecans . . . 
English walnuts 

Sugar and Sweets 
Sugar . . . 
Honey . . 
Maple syrup 
Molasses . . 
Corn syrup . 
Gingerbread, plain 

Sponge cake (2 eggs, hot 


i cup 
3 medium 

2 medium 
2 slices 

1 in. thick 

3 to 4 large 

f cup 
1 cup 
f cup 

9 halves 
3 to 4 
3 large 

4 medium 
i cup 

12 to 15 

20 to 24 


12 meats 

8 to 16 





1 Xlf 
3 X2f 
X I'm. 































Adapted, by permission, from An Analysis of Instruction for Habits 
and Practices in Health and Accident Prevention prepared by E. 
George Payne (Lyons & Carnahan, publishers). 

Directions. The teacher should go over the outline point by point 
and explain any items upon which the students wish help. The habits 
and practices may be checked at any time, near the beginning and 
the end of each semester. The scoring should be recorded in the 
biology note book. Each student should aim to make his report as 
accurate as possible. 

Directions for Scoring. 

1. Allow full value or nothing for each item. 

2. Practice in any item does not mean that there can never be an 
exception. For instance, if a boy or girl is kept up one night a week 
beyond his regular, hour of retiring to attend a moving picture show, 
nothing should be allowed for the first item under regularity. On 
the other hand, should there be an imperative reason for keeping him 
up later than the regular hour on an occasion of special nature, he 
may receive full credit. But if such occasions occur often or regu- 
larly, he should be given no credit. 

3. In scoring X and XI the boy or girl should be given full credit 
for items with which he has had no experience. For instance, some 
children would have no incentive to play on railroad tracks, because 
there would be none in their vicinity. 

4. Add the scores and compare with the maximum of 500. 


I. Food 

Drink from a pint to a quart of milk every day 3 

Eat bread and butter every meal 5 

Eat some fruit every day (fresh, dried, or preserved) .... 5 



Eat some green, leafy vegetable every day (spinach, lettuce, 

kale, etc.) 5 

Eat some starchy vegetable every day (as potato) 3 

Eat a cooked cereal for breakfast daily 2 

Eat meats but once daily » 2 

Eat candies, cakes, etc., only as dessert 4 

Quantity — Check with results determined in personal dietary work 20 
Food Requirements in Calories — Age — Sex 




Total Cal. 

Protein Cal. 

Energy Cal. 

Total Cal. 

Protein Cal. 

Energy Cal. 









Eat a warm breakfast every morning 2 

Eat something warm for lunch (as soup) 3 

Eat meals every day at the regular hour and in regular amounts . 3 

Do not eat candies, cakes, ice-cream, etc., between meals . . 3 
If hungry eat some bread and butter. Do not eat within two 

hours of another meal 3 

Manner of eating 

Eat slowly in a calm, unexcited frame of mind '. 5 

Chew all foods thoroughly 5 

Engage in pleasant conversation with the family 5 

Tell a story or anecdote or interesting incident of the day . . 5 

II. Am 


Breathe deeply — take ten deep breaths before open window 

night and morning 4 

Breathe always through the nostrils, not tnrough the mouth , 5 


Bedroom air 

Sleep with windows well open every night . 5 

Do not sleep in draft — use window boards if necessary . . 3 

Air bedroom every day 4 

Schoolroom and study room 

See that room where you live or study is properly supplied with 
fresh air 5 

Time in open air 
Spend from two to three hours daily in exercise in the open air . 4 

Do Not Smoke 10 

III. Drink 

Drink four to six glasses of water every day 2 


Drink a glass of water on rising in the morning 1 

Drink two glasses of water every forenoon at regular times . 1 

Drink two glasses of water every afternoon at regular times . 1 


Do not drink out of a cup used by some one else 5 

Drink only pure water from the fountain or out of a clean cup 4 

Do not drink cold water while overheated from play or work . 3 

Do not drink water containing cracked ice 2 

Tea and coffee 
Do not drink tea or coffee 9 

IV. Exercise 

Two hours of out-door exercise daily. Run, skate, hike, swim, 
or play tennis, baseball, basket ball, volley ball, hockey, or 

any other game. 20 

Only light exercise should be taken one half hour before each 
meal or one. hour after each meal 10 

WH. FITZ. — AD. BIO. — 35 • 


V. Relaxation and Rest 

Amount of Sleep 15 

Sleep needed (Sleep alone) 




13 years 

14 years 

15 years 


16 years 

17 years 

18 years . . . . . . 


Regularity of sleep 

Go to bed at same hour every night 5 

Get up at same hour every morning 5 

Manner of sleep 

Sleep on the side, mainly the right side 3 


Use small pillow .... 1 

Cultivate a hobby that will be of lasting benefit 10 

Read good books and magazines regularly 5 

Be punctual to all engagements 5 

VI. Posture 


Sit erect while conversing v . ..... . 3 

Sit erect while studying and writing 3 


Stand erect with chest forward, head high 3 

Walk with erect carriage, feet pointing directly forward ... 3 
Carry books in hands, with arms straight 1 

VII. Cleanliness 
Hands and nails 

Wash hands before each meal 10 

Clean finger nails once every day 5 

Keep hands and nails clean and cuticle pushed back at all times 9 

Keep nails out of mouth — do not bite the nails 5 


Teeth, mouth, head 
Clean teeth, mouth, and tongue morning and night .... 5 

Do not put fingers, pencils, etc., in the mouth ^3 

Do not dampen fingers in the mouth to turn pages of a book . 3 
Do not lick postage stamps or envelopes . 3 


Take a tub bath twice every week ! 10 

Take a morning shower 5 

Always use an individual towel 5 

Bowel movement 

Have a bowel movement regularly every day 10 

Do not take drugs or medicine for this. Depend solely on food, 
water, exercise, and habit 10 

VIII. Clothing 

Keep clothing well dusted and properly cleaned 5 

Keep dresses and hose properly mended 4 

Wear clean hose every day 4 


Wear warm, porous clothing in winter 3 

Wear light, porous clothing in summer 3 

Wear shoes with broad heels, and of sufficient length .... 4 


Put on a wrap when sitting down after exercises 3 

Keep clothing properly aired . 3 

Do not sleep in clothing worn during the day 5 

Always have a clean handkerchief 3 

IX. Home Study 

In general, study at the same time each day, preferably early 
evening •■ 2 


Use a steady and sufficient artificial light. Avoid a glaring 
light 1 


Have a quiet room for study. Avoid family conversations, 
radio, etc 4 

Avoid movies and parties during the school week 2 

X. Safety Habits 
In the streets 

Look in both directions before crossing the streets 3 

Go straight across the street and at the crossings only ... 3 

Do not tarry in the street but cross promptly 3 

Help younger children to cross the street safely 3 

Do not play on railroad tracks 3 

Do not handle dangling wires or come in contact with electric 

wires 5 

Do not ride on the outside of street cars 3 

Do not beg rides on autos 5 

Do not climb on trucks and wagons 3 

At home 

Be careful about the use of matches ; keep them in a safe place 2 
Be careful about the use of kerosene and other inflammable 
materials ; keep them in a safe place ; do not start a fire with 

them 2 

Be careful always in using the gas range 3 

Be sure electric wires are disconnected before touching them . 3 

Be careful about the stairways and fire escapes 3 

Do not climb on chairs, tables, and step-ladders unless neces- 
sary, and then only after examining them 3 

Do not place heavy objects or sharp instruments where they 

may fall upon some one • 3 

Do not leave chairs or other objects where some one may 
stumble over them in the dark 3 


Do not start your automobile engine in a closed garage ... 3 
Have an annual health examination and have remediable defects 

corrected ? 10 

Visit the dentist every six months 5 

At school 

Do not hurry down the stairways 3 

Do not run in the halls 3 

Look before going in and out of doors, and do not rush ... 3 

Take one step at a time on stairways 3 

At play 

Do not run on busy traffic streets in play 3 

Do not play near high places or on rough grounds .... 3 

XI. Service — Social and Civic Habits and Practices 

Service at home 

Give some help to your mother or father every day .... 5 

Keep shoes shined, clothes brushed 5 

Go on errands cheerfully 5 

Service at school 

Serve on Health or Safety Committees 5 

Call attention in every case to children who violate health or 

safety practices . ...... 5 

Service to the community 

Notify the Police Department of any obvious violations of 

ordinances 3 

Notify the Fire Department in case of fire 3 

Notify the Health Department of menaces to health in the 

neighborhood 5 

Notify the Street Department of holes in the street, obstruc- 
tions, unclean alley in neighborhood, etc 3 


o W 

































-* . 















































































































































79 * 






































































' 63 











* 64 































■ 67 





























































Age — years 















Average (Shorl 
















height jMedi 
















(inches) iTall 















Average [Sho 















annual {Met 















gain (lbs.) ITall 














Baldwin, B. T., and Wood, T. D., Weight-Height-Age Tables. American Child Health 
Association, New York, N. Y. 

















































































































































































































































































































Age- Years 














Average (Shoi 















Height {Mec 















(inches) [Tall 














Average fSho 














Annual { Mec 














Gain (lbs.) ITaU 













Baldwin, B. T., and Wood, T. D., Weight-Height- Age Tables. American Child Health 
Association, New York, N. Y. 





(Now being tried in 30 schools) 

I. Cell Studies 

1. Study of the living green cell ; illustrated in Spirogyra or Elodea. 

(a) Structure ; microscopic study. 

(b) Functions ; emphasis on food-manufacture. 

(c) Adaptations to environment. 

2. Study of the living animal cell ; illustrated in amoeba or Para- 

(a) Structure ; microscopic study. 
(6) Functions. 

(c) Adaptations to environment. 

(d) Comparison of plant and animal cells as to structure and 

3. Study of the typical or generalized cell. 
(a) Structure. 

(6) Comparison and nature of protoplasm. 

4. Cell division, 
(a) Amitosis. 

(6) Mitosis ; names of phases optional. 

5. Association of cells in tissues and organs. 

(a) Study of human tissues ; four of the following required : 

epithelial, muscle, bone, connective, nerve. 
(6) Differentiation, specialization, physiological division of 

(c) Comparison of tissue cell with independent plant or animal 


6. History of cell theory ; contributions of any three of the follow-^ 
ing : Hooke, Malpighi, Leeuwenhoek, Schleiden, Schwann, Max 


II. Nutrition 

1. (Optional) Study of the frog as an introduction to human 

(a) Identification of systems of organs. 
(6) Appearance and location of organs. 

2. Study of metabolism in man. 

(a) Digestion. 

1. Purpose. 

2. Foods; uses of different nutrients; include vitamins 
and deficiency diseases ; omit planning of diets and food 

3. Alimentary canal and digestive glands. 

4. Enzymes, intermediate products, end products. 

5. Experiments showing digestion. 

6. Peristalsis. 

7. Hygiene of digestion. 

(b) Absorption. 

1. Purpose. 

2. Adaptations. 

(c) Circulation. 

1. Purpose. 

2. Composition of blood ; function of each part ; clotting. 

3. Organs of circulatory system. 

4. Course of blood; changes in composition in various 

5. Lymph and lymphatic system. 

6. Hygiene of circulation. 

7. Discoveries of Harvey, Malpighi, and Leeuwenhoek on 
the blood and circulation. 

(d) Assimilation. 

(e) Respiration. 

1. Brief study of air passages. 

2. Emphasize cell respiration. 

(f) Secretion. 
1. Duct glands. 

• < 


2. Endocrine glands and hormones; secretin, pancreatic 
hormone; secretions of thyroid, adrenal, and pituitary 
(g) Excretion. 

1. Formation of principal waste products; carbon dioxide, 
water, urea, uric acid. 

2. Organs of excretion. 

3. Hygiene of excretion. 

(h) Summary of metabolism of carbohydrates, fats, and proteins. 

3. Parasitism, saprophytism, and symbiosis. 

(a) Definitions and examples; omit all detailed study, except 
as included under bacteria and malarial parasite. 

(6) Life history and importance to mankind of one parasite ; 
malarial organism suggested. 

(c) Effect of parasitism on host and on parasite. 

4. Comparative study of different types of nutrition. 

III. Irritability 

1. A function of protoplasm; illustrated in protozoa. 

2. Tropisms in plants ; geotropism, hydrotropism, phototropism ; 
demonstrate, unless covered in elementary biology. 

3. Irritability in man. 

(a) General structure and functions of the nervous system; 
emphasis on function. 

1. Central nervous system. 

a. Brain; including cerebrum, cerebellum, medulla, 

and their general functions. 
6. Spinal cord and its general functions, 
c. Nerves, cranial and spinal ; omit names of individual 


2. Autonomic system. 

3. Neurons, cranial and spinal ; omit names of individual 

(6) The types of nervous reactions. 

1. Inborn automatic activities; reflex actions and the 
reflex arc. 


3. Bacteria as useful organisms, 
(a) In food preparation. 

1. Ripening and flavoring of dairy products. 

2. Making of vinegar. 
(6) In agriculture. 

1. Decay. 

2. Nitrification ; comparison with dentrification. 

3. Nitrogen ; fixation. Nitrogen cycle. 

4. Rotation of crops. 

(c) In other industries and arts. 

1. Retting of flax. 

2. Tanning of leather. 

4. Bacteria as harmful organisms. 

(a) In decay of foods (optional) ; methods of food preservation. 
(6) In causing disease. 

5. Pathogenic microorganisms ; study of the following diseases : 
diphtheria, tuberculosis, colds, typhoid fever, smallpox, tetanus, 
hydrophobia, malaria, yellow fever, focal infections ; to bring out 
the following principles : 

(a) Sources of infection ; contact, food, and drink, air, human 

carriers, insect carriers. 
(6) Bacterial poisons ; toxins, ptomaines. 

(c) Methods of protections; skin, adaptations of respiratory 
tract, white corpuscles. Antibodies (antitoxins, lysins, 
agglutinins, and opsonnis). 

(d) Methods of immunity and immunization. 

1. Active; vaccination, toxin-antitoxin innoculation ; 
Pasteur treatment. 

2. Passive; antitoxin treatment. 

3. Tests for immunity ; Schick test. 

(e) Description of the causative organism, general character 
of disease, symptoms, diagnosis, prevention, and treatment 
(where discussion is feasible) for each of the diseases. 

(/) Work of the Department of Health. 

(g) Biography; scientific contributions of Jenner, Lister, Pas- 
teur, Koch, Metchnikoff, Ehrlich, 


Ability, families of inferior, 358-362; 
families of superior, 356-358 

Abrasion, meaning of, 168 

Absorption, digestion and, 125-141 ; 
from large intestine, 138 ; from small 
intestine, 136-138 ; in organism, 34 ; 
in green cell, 34-36; stomach, 136 

Acidopholus milk, 140 

Acne, definition of, 175 

Acquired reactions, 220-221 

Acromegaly, 197 

Active immunity, acquiring, 507-508 

Activities, acquired automatic, 220-221 ; 
inborn automatic, 215-217 ; kind of 
mental, 215; reflex, 215-216; volun- 
tary, 219-220. See also Nervous 

Adam's apple, 179 

Adaptability, relation to health, 414-415 

Adaptations, of tissues, 88-89 ; of higher 
plants, 69-72 

Adaptive processes, in organisms, pur- 
pose of, 34 

Addison's disease, causes of, 198-199 ; 
characteristics of, 198 

Adenoids, 179-180 ; colds result of, 475- 

Adipose tissue, use of, 81-82 

Adolescence, table of, 302 

Adrenal glands, effect of secretion on 
body, 197-198; location of, 197; 
relation to arterial pressure, 197-198. 
See Addison's disease 

Adrenaline, 197 ; use of, 199 

Adrenin, effect on body, 197-198 

Afferent axon, 209 

Agar slant, inoculation of, 398 ; prepara- 
tion of, 396-397 

Age, chronological, 229; mental, 228; 

. of earth, 378, 381 ; of science, 1-3 

Agglutination test, 465-466, 467 

Agglutinins, 465, 467, 469; in typhoid, 
467 ; production of, 501 ; to determine 
presence of, 465-466 ; use of, 501 

Agriculture, bacteria in, 405-411 

Air, composition of expired, 183 ; com- 
position of inspired, 183 ; tidal, 183 

Air sacs, 179 

Air tubes, 179-180 

Alcohol, effect on circulation, 168-169 ; 
effect on nervous system, 237 

Algae, characteristics of, 33 ; classified, 

Alimentary canal, laboratory study of, 

in frog, 116; in man, 117; description 

of man's, 118, 119-120 
Alkali, laboratory problem, effect on a 

fat, 131-132 
Allosaurus, prehistoric reptile, descrip- 
tion of, 383 ; restoration of, 372 
Alveolar theory, of nature of protoplasm, 

Amitosis, meaning of, 60 ; process of, 60 
Amoeba, assimilation in, 44 ; behavior of, 

44 ; digestion of, 43 ; ingestion of, 43 ; 

irritability of, 44-46 ; laboratory 

problem on study of, 42-43 ; life 

functions of, 43 ; locomotion of, 46 ; 

regeneration of, 56 ; reproduction of, 

44, 248 ; respiration of, 44 
Amphibia, 525-526 
Amylase, an enzyme, 38, 131 ; amylopin, 

Anabolism, in cell, activities in, 60; 

meaning of, 59, 187 
Anaemia, causes, 146, 167 ; symptoms, 

Anaphase, stage in cell division, 61, 62 
Ancestry, influence in development, 310- 

Andalusian fowls, heredity in, 318-320 
Andrews, Roy Chapman, on Mongolian 

expeditions, 385-387. See frontispiece 
Angiospermae, meaning of, 520, classi- 
fied, 520 
Animal, and plant breeding, 343-354 
Animal cell, typical, 42-52 
Animal passage, meaning of, 508 
Annelida, classified, 522-523 ; meaning 

of, 522 
Anopheles, spread of malaria by, 482-484 
Ant eater, giant, 512 
Anthozoa, 522 
Antibodies, agglutinins, 501 ; antitoxin, 

501 ; lysins, 501 ; opsonins, 500, 502 ; 

precipitins, 501-502 ; production of, 

146, 501 ; use of, 146 
Antiseptics, laboratory problem to show 

effect on growth of bacteria, 401-402 ; 

use of, 4 
Antitoxin, discovery of diphtheria, 451- 

452 ; kinds of, 501 ; preparation of 




diphtheria, 451-452, 456 ; preparation 
of tetanus, 461 ; produced in body, 
501 ; scarlet fever, 459 ; standardizing, 
456 ; use of, 501 

Aorta, 153, 159 

Aphids, 271 

Appendicitis, 135 

Appendix, vermiform, 135 

Arachnida, 524 

Archaeopteryx, earliest known bird, 383 

Archiannelida, 523 

Aristotle, classification by, 510 ; Father 
of Biology, 10 ; idea of evolution, 371 ; 
work of, 11 

Arterial blood, 144 

Arteries, direction of flow of blood in, 
154, 156; functions of, 154, 156; 
hardening of, 168 ; meaning of name, 
153, 156; regulation of size of, 156; 
"rupture of, 168; structure of walls of, 

Arterioles, 159 

Arteriosclerosis, causes of, 168 

Artery, pulmonary, 153 

Arthropoda, classified, 517; 523-524; 
meaning of, 523 

Artificial selection, importance in animals 
and plants, 352 

Ascaris, diagram of mitosis of egg of, 61 

Asexual reproduction, by vegetative 
propagation, 255-263 ; of algae, 247- 
248 ; of bacteria, 247 ; of hydra, 248, 
249-250 ; of protozoans, 248 ; of yeast, 

Assimilation, a life process, in amoeba, 
44 ; in green plants, 39-40 

Asteroidea, 522 

Asthma, cause of, 477; treatment of, 
477 ; vaccination for, 477 

Auricles, of heart. See Heart 

Autonomic nervous system, description, 
210 ; diagram of, 210 ; functions of, 
210-211 ; importance in nervous 
activities, 221-222 ; relation to cen- 
tral nervous system, 210-211 

Aves, animals of class, 526 

Axon, of nerve cell, 86, 87 

Bacilli, form of bacteria, 392 

Bacillus, acidopholus, 140; bulgaricus, 
140 ; typhoid, 465 

Bacteria, 391-411; action on body, 
494-495 ; aerobic, 393 ; anaerobic, 
393; beneficial activities, 403-411; 
cause of pus, 494 ; cause of disease, 494- 
495 ; carried through lymphatics, 500 ; 
colony of, 395 ; conditions necessary 
for growth, 399-400 ; cultures of, 396- 
397, 398 ; denitrifying, 407 ; destruc- 
tion of white corpuscles by, 500, 
504-505; effect of temperature on, 

399, 499; forms of, 392-393; func- 
tions of, 393-395 ; growth in milk, 
140; growth of, 398-399; in agri- 
culture, 405-411 ; in our body, 494- 
500; in air, 495-496; 475; in dust, 
473 ; in eyes, 496 ; in food preparation, 
403-404, 405 ; in industries, 403-404 ; 
in lymph and lymph nodes, 166-167, 
500 ; laboratory problem to determine 
bacterial content of milk, 401 ; labora- 
tory problem to determine number of 
bacteria in air, 400-401 ; laboratory 
problem to show effect of antiseptics 
on growth of, 401-402 ; media for 
cultivation, 396-397; methods of 
entering, body, 495-496; methods of 
identifying, 395-396 ; nitrifying, 406 ; 
nitrogen-fixing, 394, 407-409; nutri- 
tion of, 394 ; occurrence of, 397-399 ; 
of decay, 406 ; parasitic, 393 ; patho- 
genic, 394 ; physiological functions of, 
393-395 ; relation to disease, 494-495 ; 
saprophytic, 391, 394; soil, 405-411; 
structure of, 391-393 

Bacterial content, laboratory problem, in 
air in various places, 400 ; in milk, 401 

Bacteriolysin, antibody, 501 ; function 
of, 465, 469 

Bacteriology, definition of, 17 

Bacteriophage, 508 

Banting, F. G., work with insulin, 199 

Beach plum, improved, 348-349, 352, 353 

Beetle, potato, effect of environmental 
conditions on, 341 

Behring. See Von Behring 

Beriberi, cause of, 98-99, 100; preven- 
tion of, 99, 100 

Bile, basis for manufacture of, 161 ; 
function of, 132 

Binet, Alfred, tests by, 228 

Binet scale, 228 

Binet-Simon Scale, Terman's revision, 

Binomial system, of classification, 510- 

Biogenetic law, 388-389 

Biology, affected by work in other 
sciences, 19 ; divisions of, 17 ; mean- 
ing of, 15 ; of to-morrow, 1-9 ; pur- 
pose of, 6-7 ; relation to chemistry, 16 ; 
relation to health, 7-8; relation to 
other sciences, 16 ; relation to physics, 
15-16 ; relation to vocations, 8-9 

Birds, egg-laying of, 299 ; food of, 299 ; 
nest-building of, 298 ; infancy among, 
298-299 ; reproduction of, 288-289 

Bishop, on vitamin E, 103-104 

Blackberry, production of white, 347- 
348, 349 

Bladder, urinary, function of, 175-176 ; 
structure of, 175 



Blastula, 286 

Bleeders. See Haemophilia 

Blood, arterial, 144 ; a tissue, 87, 146 ; 
circulation of, 143, 153-161 ; clotting 
of, 148 ; composition of, 145 ; corpuscles 
of, 87-88, 147-148 ; count, 147 ; course 
of, 159-161 ; early drawing of circula- 
tion of, 151 ; functions of, 145-146, 

150, 162 ; grouping of, 148-149 ; heat 
of, 150 ; importance of, 143-150 ; lab- 
oratory problems on study of, 87, 
143-144 ; laboratory study of cor- 
puscles of, 144-145 ; laboratory study 
of serum of, 144 ; necessity of circu- 
lation of, 149-150 ; need of water to, 
167 ; of frog, 89 ; of man, 88 ; oxygen- 
ated in lungs, 179 ; properties of, 145- 
146 ; serum of, 144 ; transfusion of, 
149 ; venous, 144 

Blood plasma, composition of, 145 
Blood platelets, function of, 148 ; struc- 
ture of, 148 
Blood serum, laboratory study of, 144 
Blood vessels, 143 ; laboratory study of, 

151. See also Arteries, Capillaries, 
and Veins 

Bone, formation of, 79 ; laboratory 
problems on microscopic structure of, 
78; laboratory study of cross struc- 
ture of, 77-78 ; proper growth of, 80 

Bone cell, diagram of, 80 

Brain, parts of, 206-207; structure of, 

Breathing, control by carbon dioxide, 
183 ; control by oxygen, 183 ; labora- 
tory problem of modifications of, 183 ; 
laboratory problem on mechanics of, 
181 ; movements of, 181-182 

Breeding, aims of, 345-351 ; artificial 
selection in, 352 ; for improved quality, 
350 ; for increased production, 351 ; 
for points, 349-350; hybridization, 
351 ; importance of animal, 344-345 ; 
353 ; importance of plant, 343-345 ; 
Mendel's experiments in, 322 ; methods 
of animal, 353-354 ; methods of plant 
propagation in, 351-353 ; results of 
close, 353-354 

Breeding experiments, of plants, by 
Mendel, 322 

Bronchi, 178, 179 

Bronchial tubes, 179 

Bronchitis, 474 

Broncho-pneumonia, predisposing fac- 
tors, 474 

Brontosaurus, restoration of, 372. See 

Brown, Robert, described movement of 
molecules, 35-36 ; observed nucleus of 
cells, 27-28 

Brownian motion, 36 

WH. FITZ. AD. BIO. — 36 

Bruise, cause of, 168 

Bryophyta, 519 

Budding, laboratory problem in yeast 
cells, 248-249 ; method of reproduc- 
tion, 248-250; of hydra, 249-250; 
of sponges, 253 

Bulbs, propagation by, 262-263 

Burbank, Luther, experimental methods 
of, 14 ; fruit improved by, 347-349 ; 
on potato blight, 344 

Calcarea, 521 

Calcium, need for, 111 

Calkins, Dr., experiments on regenera- 
tion, 56 

Calorie, defined, 93 ; needs, 105 

Calorimeter, measurement of human 
energy by, 189 

Calyx, of flower, function of, 274 

Canning, 400 

Capillaries, broken, 168; function of, 
157 ; in lungs, 179 ; pressure in, 157 ; 
structure of, 157 

Carbohydrates, manufacture of, 36-37 ; 
metabolism of, 188; constituents of, 

Carbon cycle, 409 

Cardiac opening. See Stomach, parts of 

Carnivora, animals of Order, 527 

Carrell, Alexis, cultivation of cells, 54- 
55 ; preparation of Dakin solution, 55 

Cartilage, functions of, 79-80 ; kinds, 79 

Catalytic agents, in digestion, 38 

Catarrh, cause of, 474 

Cebidae, 527 

Cell, absorption in green, 34-35 ; amitosis 
in, 60 ; assimilation in, 39-40 ; cultiva- 
tion of, 54-55 ; digestion in green, 38 ; 
direct division of, 41, 60; discovery 
of nucleus of, 27-28 ; division of, 41 ; 
excretion in green, 40 ; food manufac- 
ture of studies of, 36-38; functions 
of green, 34^0; history of, 27-33; 
growth and division, 40, 41, 53-64; 
inclusions in, 37 ; indirect division of, 
60-63 ; irritability in green, 40-41 ; 
key to all biological problems, 29-30; 
laboratory study of Elodea, 28-29; 
laboratory study of onion, 25-26; 
laboratory study of narcissus leaf, 30- 
31; laboratory study of Spirogyra, 
31-33 ; mitosis of, 60-63 ; named and 
described by Hooke, 27-28; nature 
and composition of, 53-55 ; primary, 
269, 285; relation to heredity, 55; 
respiration in green, 38-39 ; resting 
and dividing, 53-64 ; sex, 269 ; somatic, 
269 ; structure of, 30 ; theory, 28, 30, 
52, 64 ; typical animal, 42-52 ; unit of 
function of organism, 30; unit of 
structure of organism, 30, 53 ; 73 ; 



57-58; wall of, 52, 58; work of all, 

Cellulose, of plant cells, 52 

Central nervous system, divisions of, 
205; functions of, 206-210; protec- 
tion of, 205-206 

Centrosome, function of, 59 ; in cell 
division, 61-62 

Cephalopoda, 523 

Cercopithecidae, 527 

Cerebellum, function of, 207; level of 
reaction in, 218, 219, 220 ; nature of, 

Cerebro-spinal nervous system. See 
Central nervous system 

Cerebrum, function of, 206-207; level 
of reaction in, 218, 220; nature of, 
206 ; position of, 207 ; size in various 
animals, 207 ; structure of, 206 

Cetacea, animals of Order, 527 

Chaetopoda, 523 

Chambers, Prof. R. H., dissections under 

• microscope by, 23, 45 ; on heredity, 55 

Chance, law of, laboratory problem to 
demonstrate, 317 

Character, dominant, 324, 333; of off- 
spring, 306-317 ; recessive, 325, 333 

Character-determiners, in chromosomes, 
55, 319 

Characters, acquired, 336-337 ; domi- 
nant, 324, 333; inherited, 336; 318- 
333 ; law of unit, 327-333 ; recessive, 
325, 333; secondary sexual, 281-282 

Chemistry, and its relation to biology, 16 

Chemotropism, shown by amoeba, 46. 
See Tropisms 

Chicken pox, effects of, 478 ; method of 
spread, 478 

Child-labor laws and eugenics, 366-367 

Chiroptera, animals of Order, 527 

Chlorophyll, in plants, function of, 36-37, 
39, 59 

Chloroplasts, first seen, 28 ; function of, 
59 ; structure of, 28 

Chordata, classified, 525-527 ; meaning 
of, 525 

Chromatin granules, function of, 57 ; 
structure of, 55 

Chromosome, changes in number, 339 ; 
number in sex cells, 270-271 

Chromosome theory, of inheritance, 331- 

Chromosomes, 55 ; behavior in cell 
division, 62 ; behavior in maturation, 
268-269, 284, 316 ; continuity of, 306, 
307 ; laboratory problem to show 
chance combinations of genes in, 317 ; 
laboratory problem to show possible 
combination of genes in, 326-327 ; lo- 
cation of genes in fruit fly, 312 ; locus 
of genes, 331 ; number in sex cells and 

body cells of various animals, 307; 
270-271; relation to heredity, 315- 
317, 324-326, 331-333 

Chronological age, 229 

Chyme, 129 

Cilia, in Paramecium, 48, 49, 50; in 
respiratory tract, 75, 179 

Circulation, of blood, 143 ; coronary, 
154 ; early investigations of the., 163- 
165 ; effect of violent emotions on, 
167 ; necessity of, 149-150 ; organs of, 
153-154 ; portal, 160-161 ; pulmo- 
nary, 160; systemic, 159-160; time 
for complete, 161. See Blood 

Circulatory system, 151-162 ; diagram 
of, 155 ; functions of, 168 ; hygiene of, 

Classification, basis of, 512-514 ; diffi- 
culties in, 511-514 ; evolution in, 517- 
518; geographical distribution and, 
573; habits and, 513-514; Interna- 
tional Commission on, 514-515; mor- 
phology in, 513 ; of plants and animals, 
518-527 ; present method of, 515-518 

Cloaca, in frog, 115 

Close-breeding, reasons for and results 
of, 353-354 

Clotting of blood, 148 

Cocci, form of bacteria, 392 

Coelenterata, classified, 521-522 ; mean- 
ing of, 521 

Cohnheim, J., experiment on transmis- 
sion of tuberculosis, 438 

Cold, a common disease, causes of, 473- 
475 ; chronic, 474 ; effects on body, 
473-474 ; predisposing factors, 474 ; 
prevention of, 475-476 ; remedial meas- 
ures, 476 ; transmission of, 474-475 

Collip, experiment with parathyroid ex- 
tracts, 196 

Conjugation, 264; of Paramecium, 49- 
50, 267-268 

Connective tissue, 81-82 

Conservation, of soil, 411 

Constipation, causes of, 139 ; prevention 
of, 139, 140 

Continuity, of germ plasm, 336 

Contractile tissue, 83 

Contractile vacuole, of amoeba, 42 ; ot 
Paramecium, 47 

Corolla, of flower, function of, 274 

Coronary circulation, 154 

Corpuscles, white, description of, 88; 
functions of, 88, 147-148 ; in infec- 
tion, 148; number of, 88, 147; red, 
destruction of, 146 ; formation of, 
146 ; function of, 88, 146 ; number of, 
88, 147 ; size of, 88 ; structure of, 88 

Cortex, of brain, areas of, 206-207, 213 ; 
functions of, 207, 213 ; structure of, 206 

Cotyledons, 278-279 



Cowpox, inoculations with, 421-423 
Cows, increased products from, 344 
Cretinism, 194 
Cretins, cause of, 194 
Criminals, heredity of, 361 
Crinoidea, 522 
Crops, rotation of, 409-411 
Crossing-over, of genes, 339, 340-341 
Crustacean, 524 ; the young of, 296 
Culex, house mosquito, 483 
Cuts, treatment of, 168 
Cuttings, method £>f vegetative propaga- 
tion, 255-256 
Cyclostomata, animals of Order, 524 
Cytoplasm, 58 ; structures found in, 57 
Cyton, of nerve, 208, 209 

Dakin solution, 55 

Darwin, Charles, 371 ; on natural selec- 
tion, 373-376 

Darwinian theory, of evolution, 373- 

Darwin's, theory of, evolution, 373-376 ; 
over-production, 374 ; struggle for 
existence, 374 ; variations, 374-376 ; 
survival of the fittest, 374 ; inherit- 
ance, 374-375 

Davenport, Charles, 355 ; work in eu- 
genics, 356 

da Vinci, Leonardo, 163-164; on fossils, 

Defecation, 135 

Demospongia, animals of class, 521 

Dendrites, 86-87 ; axon, 208 

Dentine, 107 

Dentrification, process of, in soil, 407 

Dermis, structure of, 172 

Development, progressive. See Organic 

Development, influenced by ancestry, 
310-313 ; influenced by environment, 

Development of species, use and disuse, 

de Vries, Hugo, experiments with eve- 
ning primroses, 337 ; mutation theory 
of, 376-377; portrait of , 335 ; theory of 
evolution, 376-377 ; mutants, 376-377, 

d'Herelle, on immunity, 508-509 

Diabetes, insulin in treatment of, 199 

Dick test, for scarlet fever, 458 

Diet, complete, 93 ; essential, 104 ; in- 
sufficient, 93 ; insufficient in min- 
erals, 95-96 ; insufficient in proteins, 
93, 95 ; investigation by McCollum on, 
93, 95 ; laboratory problem on per- 
sonal, 105; relation of teeth to, 111— 

Digestion, and absorption, 125-141 ; 
chart of chemical, 134; hygiene of, 

138-139; in mouth, 120-121; in 
plants, 38 ; in small intestines, 132- 
133, 135 ; laboratory problem of rela- 
tion of size of protein food to time of, 
126 ; laboratory problem of relation of 
different animal proteins to, 127 ; life 
function of amoeba, 43 ; meaning of, 
117-118; process of, 117-119; sali- 
vary, 121-122, 130; time necessary 
for, 133, 140 

Digestive organs, of frog, 114-116, 117; 
of man, 116-117, 119 

Digestive system, 114-123; function of, 
117; laboratory study of the frog's, 
114-116; laboratory study of man's, 

Dinosaur, amphibian, 383 ; eggs of, 
306 ; restoration of, 372 

Diphtheria, ages most susceptible to, 453 ; 
causes of, 453-454; diagnosis, 457; 
discovery of active immunity to, 452-. 
453 ; discovery of antitoxin of, 451- 
452 ; effect on the body, 454 ; history 
of, 450 ; isolation of organism of, 
450 ; isolation of toxin of, 451 ; pre- 
vention of, 457-458 ; Shick test of 
susceptibility, 453 ; transmission of, 
454-455 ; treatment of, 455-457 

Disease, and health, 413-414 ; and men- 
tal poise, 502-503 ; causes of, 494 ; 
due to bacteria, 445, 455, 459, 482, 
492 ; due to physical agents, 473 ; im- 
munity of animals to, 345 ; immunity 
of plants to, 347 ; inheritance of, 368- 
369 ; safeguards of the body against, 
496-503 ; caused by toxin, 450-451, 458 

Division, cell, process of, 41 ; purpose of, 

Division of labor, physiological, 66-67 

Division, reduction. See Maturation 

Dominance, complete, 323-324 ; incom- 
plete, 318-321; meaning of, 323; 
Mendel's or Mendelian law of, 322-324 

Dominant characters, 323-324; list of, 

Dogs, developed from common ancestor, 
310, 311 

Duck bill, 384, 513 

Duct, thoracic, 165 

Ductless glands, 191-201 ; adrenal, 197- 
199 ; pancreas, 199 ; parathyroid, 196 ; 
pineal, 200; pituitary, 196-197; re- 
productive, 200-201 ; secretions of, 
191-192 ; spleen, 200 ; thymus, 199- 
200 ; thyroid, 192-195 

Dujardin, protoplasm named by, 28 

Dwarfism, 197 

Earth, age of, basis for estimate of, 378- 
381 ; calculations of, 378 ; evidences 
of, 378-379, 380 



Echinodermata, classified, 522 ; mean- 
ing of, 522 

Echinoidea, 522 

Ectoderm, development of, 286 ; of 
embryo, 286 ; systems formed from, 286 

Edentata, 526 ; ant eater, 512 

Education, and eugenics, 365 ; health an 
objective of, 415-417 

Edwards, Jonathan, family of, 357 

Effector, response activity of, 209 

Egg cell, characteristics of, 268 

Eggs, differ from seeds, 281 -, of insects, 
281 ; of birds, 281 ; production by 
frog, 284-285 

Ehrlich, portrait, 504; theory of im- 
munity, 505-506 ; work of, 14 

Elasmobranchii, animals of Order, 524 

Elastic tissue, use of, 81 

Elodea, diagram of, 30; laboratory 
study of cells of, 28-29 

Embryo, development of seed, 278-279 ; 
protection of, in lower animals, 295- 
296; 288-289; in insects, 297-298; 
in mammals, 299-301 ; in man, 301 

Embryo sac, 274, 276, 277 

Embryological evidence, of evolution, 
388-389 ; similarities in development of 
embryos of vertebrate animals, 388-389 

Emotions, dangers of violent, 167 

Enamel, of teeth, 107 

Encystment, of protozoans, meaning of, 
253 ; why formed, 253 

Endocrine glands, 191 

Endoderm, of embryo, 286 

End-organs, in skin, functions of, 173 

Endosperm, 278, 279; in grains, 279; 
systems formed from, in embryo, 

Endotoxins, meaning of, 495; of tuber- 
culosis, 442 ; of typhoid, 465-466 

Energy, human, measured by calorim- 
eter, 189 ; kinetic in plant cells, 39 

Enterokinase, use in digestion, 133 

Environment,' effect on ancestral traits, 
313-315 ; influence on development of 
animals, 308-310; influence on de- 
velopment of plants, 308, 309 ; meth- 
ods of improving, 364-367 ; versus 
heredity, 369-370 

Evironments, effect of different, 308 

Enzymes, digestive action of, 128, 131 ; 
function in plants, 71 ; in gastric juice, 
128 ; in intestine, 132-133 ; in plant 
cells, 38 ; in saliva, 121 ; of pancreatic 
juice, 131 ; specific action of, 128-129, 

Epidermis, laboratory problems on 
study of leaf, 30-31, 67; laboratory 
problem on cross section of leaf, 67- 
68; outer layer of skin, 171, 172 

Epiglottis, use of, 122 

Epithelial cells, laboratory problem on 
75 ; shape of, 75 

Epithelium, 75-77 

Erepsin, 132 

Esophagus, 122, 123 

Essay on Population, Malthus, 343 

Eugenics, 355-370 ; child labor laws and, 
366-367 ; compulsory education and, 
365; immigration and, 367-368; 
laborer compensation laws and, 365 ; 
movement founded and named, 355 ; 
need for understanding, 363 ; relation 
of marriage to, 355-356; 363-364; 
Second International Congress of, 355 ; 
versus euthenics, 368 ; vocational 
guidance and r 367 ; widows' pensions 
and, 365-366 

Eugenics Laboratory, at Cold Spring 
Harbor, 356 ; symbols used in chart 
making at, 356 ; work done by, 362- 

Eustachian tubes, 122 

Euthenics, consists of, 365-368 ; mean- 
ing of, 355, 362 ; versus eugenics, 368 

Evans, on vitamin E, 103-104 

Evening primroses, de Vries' experiments 
with mutants of, 337 

Evolution, organic, Aristotle's idea of, 371 ; 
Darwin's natural selection theory of, 
373-376 ; de Vries' mutation theory of, 
376-377 ; embryological evidences of, 
388-389 ; geographical evidences of, 
385-386 ; history of, 371 ; geological 
evidences of, 381-384 ; in plants, 389 ; 
Lamark's use and disuse theory of, 
371-373 ; meaning of, 371 ; morpho- 
logical evidences of, 386, 387 ; vestigial 
evidences, 387-388 

Evolutionists, beliefs of, 37i 

Excretion, definition of, 170 ; hygiene of, 
174-175, 176 ; importance of, 170 ; of 
man, 170-176 ; process in a green cell, 

Excretory organs, 170-176 

Exotoxins, 495 ; in diphtheria, 451 ; in 
scarlet fever, 458 ; in tetanus, 459 ; 
in tuberculosis, 442 

Experimentation, modern methods of, 15 

Expiration, meaning of, 182; process of 
in man, 182 

Fi, defined, 319 

F 2 , defined, 319 

Families, of inferior ability; 358-362; 
of superior ability, 356-358 

Fatigue, cause of, 232 ; effect of, on 
individual, 232-233 ; how to over- 
come, 233 ; test of muscles of frog for, 

Fats, laboratory problem of effect of 
alkali on, 131-132 ; metabolism of, 190 



Fermentation, during reproduction of 
yeast plants, 250-251 

Fertilization, adaptations for, in plants, 
293 ; double, 278 ; external and in- 
ternal, 283, 288; in frog, 270-271, 
283-284, 285; in higher plants and 
animals, 268, 269 ; in plants, 277-278 ; 
significance of process, 285 

Fever. See Yellow fever, Typhoid 

Fibrinogen, in blood, 143, 145, 148 

Fibrous tissue, functions of, 80-81 

Fibrovascular bundles, structure of, 70 

Filament, of Spirogyra, 32 

Filter passers, 393 

Filterable virus, 393 

Fish, care of young, 296 ; spawning of, 

Fission, binary, a form of cell division, 
44, 247-248 

Fixation, of nitrogen, by bacteria, 407- 

Flanders, on intelligence testing, 239-231 

Flatworms. See Platyhelminthes 

Flax, useless parts removed by bacteria, 

Flowers, calyx of, 274 ; corolla of, 274 ; 
essential organs of, 274 ; production of 
female gamete, 276-277; production 
of male gamete, 275-276 

Fluid, tissue, 165 

Foam theory, of nature of protoplasm, 54 

Focal infection, common, 478 ; defined, 
174-175, 477; effect of, 477; pre- 
vention, 478 

Focusing, miscroscope, rules for, 24 

Folds, in small intestine, 136 

Follicle, hair, 173 

Food, bacteria in preparation of,* 403- 
404 ; definition of, 91 ; improvement 
in quantity and quality of, 344-345 ; 
manufacture in green cells, 36-38 ; nu- 
trients, 91-104 ; of plant cells, 36 ; pres- 
ervation of, 399—100 ; storage of, 71 

Food manufacture, in green cells, 36-38 ; 
process of, 36-37 ; the products formed 
in, 37-38 

Food nutrients, 91-104; table of, 94 

Foods, containing mineral, 96 ; contain- 
ing proteins, 95 ; energy value of, 92 ; 
fuel value of, 92 ; importance of, 91 

Formation of fruit, 279 

Fossils, formation of, 378, 381 ; state of 
perfection, 381 

Four-o'clocks, heredity of, 320-322 

Freak. See Mutants 

Frog, breeding habits of, 282-283 ; de- 
velopment of, 285-286; laboratory 
study of alimentary canal of, 116 ; lab- 
oratory study of internal organs, 114- 
116; life history of, 287; produced 
parthcnogenetically, 271-272 ; produc- 

tion of eggs, 284-285; production of 
sperms, 285 

Fruit, function of, 279 

Fruit fly, location of genes in chromo- 
somes of, 312, 332 

Fuel, in plants, 37 

Functions, of green cells, 34-41 

Fungi, characteristics of, 33 ; classified, 
518-519 ; meaning of, 33 

Galen, idea of circulation, 163, 164 

Galton, Sir Francis, application of statis- 
tical method to study of human 
heredity, 357 ; interest in eugenics, 

Galvanotropism, shown by amoeba, 46 

Gametes, female, 266; formation of, 
264 ; male, 266 ; production in flower- 
ing plants, 275-277 

Ganglion, 210, 211 

Gastric juice, cause of flow of, 120; 
composition of, 125-126; effect on 
protein, 126; enzymes in, 128; func- 
tions of, 128 ; laboratory problem, how 
protein is affected by, 126 ; secretion 
of, 127-130 

Gastropoda, 523 

Gastrula, 286 

Generation. See Spontaneous genera- 

Genes, change in character of, 339-340 ; 
character of, 316; combination in sex 
cells, 332-333 ; crossing-over of, 339, 
340-341 ; definition of, 306 ; double, 
331 ; functions of, 306 ; laboratory 
problem to show possible combinations 
in cells, 336-337 ; location in chromo- 
somes of fruit fly, 312, 332 

Geographical evidences, of evolution, 
habitats of animals, 385 ; ' Mongolian 
Expeditions, 385-387 

Geological evidences, of evolution, 381- 
384 ; fossils, 379, 381-382 

Geotropism, 203 

Germ carriers, 397-399, 454-455, 482 

Germ plasm, causes of variation, 336- 
337, 339-342; continuity of, 336; 
effect of environment on, 341-342 ; 
theory of, 335-336 

Germicide, 402 

Germinal variations, transmitted, 312, 

Germination, 279 

Gigantism, cause of, 197 

Gilbert, W., influence on Harvey, 163 

Gills, tadpole, 287 

Gland, oil, 173; sweat, 171, 173 

Glands, ductless, 191-201 ; endocrine, 
191 ; experiment of grafting, 201 ; 
meaning of, 118; location in man, 
192 ; location in a rat, 193 ; position 



of gastric, 125 ; rate of secretion of, 
127; regulation of secretion, 127-128; 
relation to digestion, 118, 119. See 
Adrenal, Intestinal, Liver, Pancreas, 
Parathyroid, Pineal Body, Pituitary, 
Reproductive, Salivary 

Granular theory, of nature of proto- 
plasm, 54 

Glottis, 122 

Glycogen, in liver, 161 

Goiter, and iodine, 194-195; districts, 
194-195; endemic, 194; exophthal- 
mic, 195 

Goldberger, Dr. Joseph, work on vita- 
min P-P, 104 

Gonads, 200 

" Goose flesh," cause of, 172 

Gorgas, eradicating yellow fever, 491 

Grafting, bud, 258; effect of, 258-259; 
in surgery, 259-260 ; process of, 257- 
259 ; propagation by, 257-260 ; stem, 
257-258 ; tongue, 259 

Greeks, contributions to science, 10-12 

Growth, of science, 10-17 ; mental, 225 

Guard cells, of stomata, 67 

Guinea pigs, in breeding experiments, 

Gymnospermae, classified, 520 ; mean- 
ing of, 520 

Habit, breaking a, 224-225 ; formation 
of, 220-221 ; meaning of, 221 

Haemoglobin, 182 ; and oxygen, 146 ; 
function of, 88, 146-147 ; in corpuscles, 

Haemophilia, 148 

Hair follicles, origin of, 173 

Harvey, William, discoverer of circula- 
tion of blood, 163, 164-165 ; influence 
of Gilbert on, 163 ; portrait of, 143 ; 
theory confirmed by Leeuwenhoek, 

Health, and adaptability, 414-415; and 
education, 415-417 ; and longevity, 
414 ; disease and, 413-414 ; measure- 
ment of, 419 ; science and, 417-419 

Health education, need of, 7, 415-417 

Heart, auricles of, 152, 154, 159-160; 
laboratory study of, 152-153 ; proper- 
ties of muscles of, 85, 152, 154 ; struc- 
ture of, 152, 154 ; valves of, 152, 154 ; 
ventricles of, 152, 154 

Hemolysin; antibody, 501 

Hepatic vein, 161 

Heredity, in Andalusian fowls, 318-320 ; 
in four-o'clocks, 320-322 ; in organ- 
isms, 333 ; methods of investigating 
human, 356-362 ; rise of knowledge of, 
318-333 ; versus environment, 369- 

Herreshoff family, inheritance of, 361 

Hexactinellida, 521 

Hippocrates,. Father of Medicine, 10-11 

Hirudinea, 523 

Holothuroidea, 522 

Hominidae, 527 

Hooke, Robert, first observer of cells, 
27 ; microscope of, 27 

Hormone, definition of, 133 ; secretin, 
133, 191 

Horse, evolution of the, 375, 376, 377 

Human heredity, difficulty in studying, 
357; methods of investigating, 356- 

Humoral theory, of immunity, 506 

Hybrid, appearance of, 319, 324; de- 
scendants of, 319-322 ; meaning of, 
319, 321 ; proportion in different 
generations, 319-322 

Hybridization, method of breeding, 351 

Hydra, reproduction of, 249-250 

Hydrochloric acid, in gastric juice, effect 
of, 129-130 

Hydrogen, a chemical element, test for, 

Hydrophobia. See Rabies 

Hydrotropism, 204, 205 

Hydrozoa, 521 

Hygiene, defects revealed by examina- 
tion, 416-417; mental, 222-237; 
of circulatory system, 167-169 ; of 
digestion, 138-141 ; of respiration, 
185 ; of skin, 174-175 

Hyphae, of mold, 264, 265 

Hypocotyl, 278 

Immigration, and eugenics, 367-368 
Immunity, 504-509; active, 452, 456, 
458 ; acquired, 501 ; antitoxins in, 
505; Ehrlich's side-chain theory of, 
506 ; establishing active, 458-459 ; 
establishing passive, 508 ; lysins in, 
505 ; meaning of active, 452 ; mean- 
ing of passive, 456 ; meaning of per- 
manent, 456 ; natural, 506-507 ; of 
animals, 345 ; of plants, 347 ; of to- 
morrow, 508-509 ; phagocytic theory 
of, 504-505 ; racial, 507 
Immunization active, 452 
Improved Beach plum, development of, 

348 T 349, 352, 353 
Impulse, nature of nerve, 222-223 
Impulses, types of, 215 
Incomplete dominance, meaning of, 319 
Indigestion, causes of, 138-141, 168 
Ingestion, a life function, of amoeba, 43 
Infancy, among birds, 298-299; among 
insects, 297-298 ; among lower ani- 
mals, 295-296; among mammals, 
299-300 ; among seed plants, 293-295 ; 
in man, 301-303 
Infection. See Focal infection 



Inferiority, conflict, nature of, 236 ; pre- 
vention of, 236 

Influenza, symptoms of, 476 ; trans- 
mission of, 476 

Infusoria, 521 

Inheritance, chromosome theory of, 331- 
333; of disease, 368-369; of varia- 
tions, 374-375 

Inoculation, smallpox, in the Orient, 420- 
421 ; introduction into England, 421 ; 
method of, 421 ; origin, 421 

Insecta, 524 

Insectivora, classified, 527 

Insects, the young of, 297 ; wasps, 297- 

Inspiration, definition of, 182 

Insulin, in treatment of diabetes, 199 

Intelligence quotient, definition of, 228- 

Intelligence, definition of, 227 ; measure- 
ment of, 228-229; of students of 
Oxford University, 357 ; relation of 
progress in school to, 229-230, rela- 
tion of vocations to, 230-231 

Intercellular materials, 74 

Intestine. See Large intestine, Small 

Intestinal gland, in relation to digestion, 

Intestinal juice, 131, 132 

Introspection, advantages of, 236 ; dis- 
advantages of, 236 

I. Q. 228—229 

Irritability, cause of, 202-203; in 
amoeba, 44HL6 ; in animals, 202-203 ; 
in green cell, 41 ; in Paramecium, 50- 
51 ; in plants, 202 ; in man, 205 

Islands of Langerhans, 198 ; location of, 
199 ; value of, 199 

Isogametes, defined, 267, 268 

Jenner, Edward, discovery of vaccina- 
tion by, 421-422 
Juke family, history of, 358-359 

Kallikak family, history of 359-360 
Kanred wheat, how produced, 347 ; 

increased yield of, 351 
Katabolism, in cell, activities, 60 ; mean- 
ing of, 59 
Kidneys, elimination of waste through, 

170; excretory function of, 175-176; 

position, 175 ; secretion of urine by, 

170, 175 ; structure of, 175 
Kitasabo, cultivation of tetanus bacilli 

by, 460 
Klebs, discovery of diphtheria bacilli by, 

Koch, discovered cause of tuberculosis, 

438-440 ; effect of his discovery, 440 ; 

experiments with guinea pigs, 439- 

440 ; portrait of, 437 ; postulates of, 
440; tuberculin test prepared by, 

Labor, physiological division of, 66-67 

Lacteals, 136-137, 166 

Lamarck, Jean de, theory of evolution, 

Lamarckian theory, of evolution, 371-373 

Langerhans, islands of. See Islands of 

Large intestine, 135 ; absorption from, 
138 ; bacteria of, 135, 140 ; bacterial 
action in, 135 ; function of, 133, 134 ; 
divisions of , 119, 135; relation to con- 
stipation, 135, 139 

Larynx, 178, 179 

Laveran, discoverer of malarial parasites, 

Laws, of inheritance (Mendel's), 322-330 

Lawton blackberry, berries produced 
from, 348, 349 

Laxatives, kinds, 139-140 ; use, 139 

Layering, method of vegetative propaga- 
tion, 260 

Lazear, work on yellow fever, 487-491 

Leaf, functions of, 70 

Learning, laws of, 223-224 

Leeuwenhoek, contribution to contro- 
versy on origin of life, 240-241 ; im- 
proved microscope, 19-20 

Lemuroidea, 527 

Levels of reactions, 216, 217 ; diagrams 
to show, 218, 219, 220 

Life, origin of, 239-245 ; ancient idea, 
239 ; a present-day theory of, 245 

Ligaments, functions, 80-81 

Lindbergh, contribution to science, 1 

Linnaean system, of classification, 510- 

Linnaeus, Carolus, system of classifica- 
tion by, 510-511 

Linin, in nucleus, 57 

Lipase, an enzyme, 38 ; steapsin, 131 

Lister, Sir Joseph, contribution to sur- 
gery, 4 

Little Club wheat, improvement of, 350 

Liver, circulation through, 160-161 ; 
function of, 132, 161 ; relation to diges- 
tion, 118; secretion of, 132; storage 
of sugar in, 161 

Locomotion, of amoeba, 46 ; of Parame- 
cium, 49 

Lockjaw. See Tetanus 

Loeb, J., on artificial parthenogenesis, 

Loeffler, isolation of diphtheria bacilli 
by, 450 

Lungs, flow of blood through, 160; in- 
fection of. See Pneumonia and Tuber- 
culosis ; laboratory problem on struc- 



ture and function of, 180-181 ; move- 
ment of, 182 ; protection of, 179 ; red 
corpuscles, 179 ; size, 182 ; structure 
of, 179 ; volume of air in, 183 

Lymph, circulation of, 165-166 ; fluid, 
137 ; pressure of, 166 ; source of, 165 ; 
spaces, 166 ; vessels, 165-166 

Lymph gland, function of, 167 

Lymph nodes, bacteria in, 167; func- 
tions of, 167; position of, 166-167; 
structure of, 167 

Lymphatic system, 163-169 

Lymphatics, 137 ; functions of, 166-167 ;, 
valves in, 166 

Lysins, use of, 501 ; kinds of, 501 

M. A., 228 

Macronucleus, in Paramecium, 49-50 

Malaria, 480-486 ; cause, 482 ; diagnosis 

of, 485 ; history of, 481-182 ; investi- 
gation of cause, 15 ; method of spread, 

482 ; nature of, 484-485 ; prevalence 

of, 480-481 ; prevention of, 486 ; 

treatment of, 485 
Malarial parasite, life cycle of, 482H:84 ; 

multiplication of, 483-484 
Malnutrition, cause of, 104 ; effect on 

embryo, 313 
Malpighi, drawing of circulation by, 151 ; 

movement of blood in capillaries first 

seen by, 164 
Malpighian layer, of skin, 172 
Malthus, effect of essay on Darwin, 373 ; 

Essay on Population, 343 
Mammalia, classified, 526-527 
Mammals, development of embryo, 299- 

300 ; food of, 300 ; infancy, 299-301 ; 

years, of dependence, 300-301, 302 
Man, infancy in, 301-303 ; protection of 

young, 30 
Manufacture, of food, by green plants, 

Marconi, Guglielmo, portrait of, 1 
Marsupialia, animals of Order, 526 
Mastication, importance of, 123 ; process 

of, 120 
Mastigophora, 521 
Mastodon, restoration of, 379 
Maturation, of egg, 264; of sex cells of 

fruit fly, 269 ; of sperm, 264 ; process 

of, 268-270 ; variation due to, 285 
McCollum, investigation on diets, 93- 

Measles, after-effects, 478 ; method of 

spread, 478 ; prevention of, 478 
Measurement, of health, 419 
Media, definition of bacterial, 395 ; for 

cultivation of bacteria, 396-397 
Medicine, early practices of, 3, 10-13 
Medulla, oblongata, description of, 207 ; 

function of, 207 

Membrane, meaning of, 75 ; mucous, 75 ; 
serous, 76 

Mendel Gregor, experiments with peas, 
322-326, 327-329; portrait of, 318; 
rediscovery of writings, 330 

Mendelian laws, of dominance, 322-324 ; 
of segregation, 324-326 ; of unit 
characters, 327-330 ; of heredity, sum- 
marized, 331 

Mental age, 228 

Mental hygiene, 227-237 

Mental poise, cause of lack of, 233-235 ; 
need of, 227, 233 ; relation to disease, 

Mesentery, function of, 77 

Mesoderm, of embryo, 286 ; development 
of, 286 ; systems formed from, 286 

Metabolism, basal, 193; in cell, 59-60; 
kinds, 187 ; meaning of, 59-60 ; of 
carbohydrates, 188 ; of fats, 190 ; of 
proteins, 188-190 

Metamorphosis, of frog, 287 

Metaphase, stage in cell division, 62 

Metchnikoff, on bacteria of putrefaction, 
140 ; theory of immunity, 504-505 

Method, modern scientific, 13-15 

Micron, unit of measurement, micro- 
scopic work, 392-393 

Micronucleus, in Paramecium, 47-50, 248 

Micropyle, of egg, 270, 276 

Microscope, 19-25 ; care of, 23-24 ; 
compound, 20 ; history of develop- 
ment, 19-20 ; Hooke's, 27 ; labora- 
tory problem on use of, 24-26 ; parts 
of, 21-23 ; rules for focusing, 24 

Milk, acidopholus, 140 ; increase in 
products of, 344 ; influence on ty- 
phoid, 467 ; laboratory problem to 
determine bacterial content, 401 

Minerals, foods containing, 96 ; insuffi- 
ciency, 95 ; need of, 95 

Mitosis, in animal cell, 61-63 ; in plant 
cell, 63, 64 ; laboratory study of, 63 ; 
process of, 60-63 

Mitral valve, of heart, 160 

Mold, laboratory problem, on spore 
formation, 251-252 ; hyphae, 251 ; 
mycelium, 257 ; rhizoid, 251 ; sexual 
reproduction in, 264, 265 ; sporangium 
of, 251-252, 253 

Molecular theory, 35 

Molecules, laboratory problem to show 
movement of, 35 

Mollusca, classified, 523 ; meaning of, 

Mollusks, the young of, 296 

Mongolian expeditions, 385-387 

Monotremata, 526 ; duckbill, 513 

Morgan, T. H., on heredity, 55; por- 
trait of, 318; work on heredity, 14; 
work on mutations in fruit flies, 312 



Morphological evidences, of evolution, in 
structure of animals, 387-388 

Morphology, meaning of, 17 

Morula, 285 

" Mother of vinegar," 391 

Mouth, of man, 120-121 ; structure of, 
120; use of, in digestion, 120-121 

Mucous, lining of nasal passages, func- 
tion of, 178 

Muscle tissue, 85-86; cardiac, 85; 
cross-striated, 85 ; function of, 85-86 ; 
structure of, 83-85 ; unstriated, 85 

Muscle, laboratory problems on struc- 
ture of skeletal, 83-84; laboratory 
problem on structure of smooth or in- 
voluntary, 84 

Muscles, antagonistic, 86 - 

Muscular action, antagonistic, 85-86 

Mutants, causes of, 377 ; examples of 
occurrence, 337-339 ; importance in 
breeding, 353-354 ; meaning of, 337 

Mutation theory, of evolution, 376 ; and 
natural selection, 377 

Mycelium, in mold, 251 

Myriapoda, 524 

Myxedema, 194 

Narcissus, laboratory study of epider- 
mis of leaf of, 30-31 

Nasal passages, removal of dust by, 178 ; 
warming and moistening air by, 178 

Natural immunity, meaning of, 506 ; of 
races and individuals, 507 

Natural selection, 373-375 ; and muta- 
tion theory, 377 ; Darwin's theory of, 
373-376; objections to theory of, 376 

Navel orange, development of, 349 

Needham, experiments to prove spon- 
taneous generation, 241 

Negri bodies, in rabies, 433, 435 

Nemathelminthes, 522 

Nerve centers, 208 

Nerve tissue, in man, 86 ; unit of struc- 
ture, 86-87 ; work of, 86 

Nerves, function of, 208-209 ; motor, 210 ; 
pathway of, 209-211 ; sensory, 209 

Nervous reactions, importance of, 223 ; 
kinds of, 215, 216-221; laboratory 
study of, 225 ; nature of, 216-217 

Nervous system, 202-214; autonomic 
portion of, 210-211 ; cellular structure 
of, 208-210; cerebro-spinal or central 
portion of, 205-210 ; effect of tobacco, 
236-237; effect of alcohol, 237; main 
subdivision of, 205 ; principle of 
operation of, 205 ; structure of, 208- 
210 ; studies of, man and other verte- 
brates, 211-212 ; the methods of study- 
ing, 212-213 

Neuron, associative, 209 ; description of, 
208 ; diagram of, 209 

Nicolaier, discovery of tetanus bacillus, 

Nitrification, process of, in soil, 406-407 
Nitrogen, cycle, 406, 410 ; fixed by 

bacteria, 406, 407-409 
Nitrogen, fixation, 407-409 
Nodes. See Lymph nodes 
Nodules, use of root, to soil, 408 
Noguchi, Hidego, 2-3 ; work on yellow 

fever, 491,492 
Nostrils, 178 
Nuclei, polar, 276, 277, 278; sperm, 

Nucleoplasm, structures found in, 57 
Nucleus, of cell, 27-28 ; endosperm, 278 ; 

egg, 277 ; generative, 275 ; tube, 275 ; 

work of, 57-58 
Nutrients, food, 91-104; definition of, 

91-92; table of, 94 
Nutrition, of Paramecium, 48-49 
Nutritive processes in organisms, pur- 
pose of, 34 

Objections, to vaccination, 423, 427 

Offspring, cause of differences among, 
315 ; character of, 306-317 

Oil glands, 173 

Onion cells, laboratory study of, 25-26 

Ontogeny, history of individual, 388- 

Onychophora, 523 

Oogenesis, meaning of, 270 

Ophiuroidea, 522 

Opsonins, effect on bacteria, 500, 502 ; 
test for amount of, 502 

Orange, navel, 349 

Organ, definition of, 73 

Organic evolution, 371-389 ; Darwinian 
theory . of, 373-376 ; embryological 
evidences of, 388-389; de Vries' 
theory of, 376-377; factors in, 371; 
geographical evidences, 385-386 ; ge- 
ological evidences, 381-384; history 
of, 371 ; Lamarckian theory of, 371- 
373 ; morphological evidences of, 386- 
387 ; vestigial evidences of, 387-388 

Organism, offspring of simple, 292-293 

Organisms, heredity in, 333 ; purpose of 
life processes in, 34 

Organs/ of digestion, 118-119; 125-135 

Origin of Species, by Darwin, 373 

Osmosis, in absorption of food, 136, 137 ; 
in root hair, 69 ; in photosynthesis, 
meaning of, 34 ; process of, 34-35 

Osterhout, on heredity, 55 

Ova, of frog, 283 

Overproduction, of species, 373 

Ovules, in flower, 274, 276-277, 279 

Oxygen, a chemical element, test for, 
16 ; importance to life, 241-242 

Oxyhaemoglobin, 147 



Palate of man, 120 

Paleontology, 378 

Palisade cells, of leaf, 67 

Pancreas, digestive secretions of, 131 ; 
internal secretion of, 199 ; relation to 
digestion, 118. See Diabetes, Insulin 

Pancreatic juice, enzymes of, 131 

Papillae, of tongue, 120; functions of, 

Parasite, definition of, 252 ; group of 
bacteria, 393-394 

Paramecium, conjugation of, 49-50, 248, 
267-268; effect of alcohol on, 50; 
irritability ofp 50-51 ; laboratory 
study of, 46-47 ; locomotion of, 49 ; 
mode of defense, 50-51 ; nutrition of 
48-49 ; reproduction of, 49-50 

Parathyroid glands, location of, 196 ; 
relation to metabolism, 196; secre- 
tion of, 196. See Tetany 

Parental care, shown by, birds, 298-299 ; 
fishes and frogs, 296 ; insects, 297-298 ; 
mammals, 299-301 ; man, 301-304 

Parenthood, development of, 303-304 

Park, Dr. W. H., inoculations with toxin- 
antitoxin, 452-453 

Parotid gland, in mouth, 121 

Parthenogenesis, 271-272 

Passive immunity, acquiring, 508 

Pasteur, Louis, 3 ; ideals of, 435-436 ; 
treatment for rabies, 430-432 ; work 
to disprove spontaneous generation, 

Pavlov, experiments on digestion, 138-139 

Payne, " Habits and Practices in Acci- 
dent Prevention and Health," 419, 
the appendix 

Peas, sweet, Mendel's experiments on 
heredity of, 322-326 ; 327-330 

Pelecypoda, 523 

Pellagra, deficiency disease, 104 

Pepsin, 128 

Pepsinogen, 128 

Peptic gland, relation to digestion, 118 

Peptone, form of protein, 128 

Pericardium, of man, 76 

Periosteum, of bone, 78 

Peristalis, described, 123 

Peritoneum, of man, 76 

Perspiration, 170 

Petri, R. J., devised Petri dish, 396 

Phagocytes, function of, 146-147, 500; 

Phagocytic theory, of immunity, 504-505 

Phagocytosis, 147 

Pharynx, 122 

Photosynthesis, meaning of, 37 ; process 
of, 36, 37 

Phototropism, laboratory problem to 
show, 203 ; shown by amoeba, 46 

Phrenology, 5, 214 

Phylogeny, history of entire race or 
group, 388-389 

Phylum, in taxonomy, 516 

Physics, and its relation to biology, 15-16 

Physiological functions, of organism, 34 

Physiology, meaning of, 17 

Pigment, in skin, 172 

Pineal body, effect of injury to, 200; 
location of, 200 

Pisces, animals of class, 525 

Pituitary gland, location of, 196; rela- 
tion to growth, 196-197. See Acro- 
megaly, Dwarfism, Gigantism 

Placenta, animals, 289, 291 ; of plants, 
274, 278 

Plant, and animal breeding, 343-353 ; 
experiments by Mendel, 322 ; organs of 
flowering, 273 

Plants, cellular nature of , 30-31 ; growth 
of seed, 293-295 ; manufacture of 
food, 36-38 ; reproduction of higher, 
273-279 ; specialization in higher, 69- 
72 ; storage of food in, 70-71 

Plasma, composition of blood, 145 

Plasma membrane, function of, 58 ; of 
cell, 32 

Plasmodium malariae. See Malarial 

Platelets.' See Blood platelets 

Platyhelminthes, 522 

Pleurae, of man, 76 

Pleurococcus, diagram of, 33 ; laboratory 
problem on, 31 ; reproduction of, 247 

Plexus, 210 

Plum, development of new species of, 

Plumcot, how produced, 349 

Plumule, 278 

Points, breeding for, 349-350 

Poise, mental. See Mental poise 

Polar, nuclei, 276, 277, 278 ; bodies, 270 

Pollen, agencies to scatter, 276 ; effect of, 
277-278; grains, 275, 276, 277; 
laboratory study of effect of sugar solu- 
tion on, 275 ; nuclear division in, 276 ; 
production of, 275 ; tube, 275, 276, 277 

Pollination, agents 'of, 293 ; artificial 
method of, 352 ; process of, 276 

Polyneuritis, cause of, 100 ; cure for, 100 

Population, Malthus' Essay on, 343 

Pore, of skin, 173 

Porifera, classified, 521 ; meaning of, 521 

Portal, circulation, 160-161 ; vein, 161 

Postulates, of Koch, 440 

Potatoes, propagation of, 350 

Pouchet, on spontaneous generation, 

Precipitins, function of, 501-502 

Preservation of food, discussed, 399 

Primates, classified, 527 ; animals of 
order of, 527 



Primroses. See Evening Primrose 

Priority, law of, 514-515 

Production, breeding for increased, 351 ; 
of new species, 347-349 

Progress, in school, relation of intelli- 
gence to, 229-230 

Propagation, methods of animal, 353- 
354; methods of plant, 352-353; of 
dahlia, 349-350 ; of potato, 350 ; vege- 
tative. See Vegetative propagation 

Prophase, stage in cell division, 62 

Protease, an enzyme, 38 ; erepsin, 132 ; 
trypsinogen, 131 

Protection, of young, 292-304 

Protein, foods containing, 95 ; formation 
of, 38 ; insufficiency of, 93, 95 ; labora- 
tory problem on effect of gastric juice 
on, 126; laboratory problem on rela- 
tion of time of digestion to size of, 
126 ; laboratory problem on rate of 
digestion of different animal, 127 ; 
manufacture of, 37-38 ; metabolism of, 
188-190 ; process of synthesis, 37-38 ; 
product of protein-synthesis, 37-38 

Proteose, form of protein, 128 

Protoplasm, cause of variety in, 306-^- 
307; cause of likeness in, 307-308; 
characteristics of, 29-30, 55-57 ; dis- 
covery of, 28 ; functions of different 
parts of, 57-60; effect of alcohol on, 
50; named, 28; specialization of, 5. 1 - 
52 ; structure of, 53-55 ; reticular 
theory of, 53-54 ; alveolar or foam 
theory of, 54 ; granular theory of, 54 ; 
variety in, 306-308 

Protozoa, classified, 520-521 

Pteridophyta, classified, 519-520 

Pterodactyl, prehistoric flying reptile, 

Ptomaines, 495 

Ptyalin, enzyme of saliva, 121 

Pulmonary, artery, 153 ; circulation, 

Pulse, cause of, 156 ; laboratory study 
on rate of, 156-157 

Punnett squares, 328, 330, 332 

Purkinje, discoverer of protoplasm, 28 

Pustules, of smallpox, 423, 425 

Pyloric valve, of stomach, 125 

Pyorrhea, cause of, 110-111 

Pyrenoids, structures in Spirogyra, 32 

Quality, breeding to improve, 330 

Rabies, cure of, 434 ; discovery of treat- 
ment by Pasteur, 430-432 ; effect on 
animals, 433 ; eradication of, 434 ; 
nature of, 432-433 ; preparation of 
vaccine for, 43 J ; prophylatic or pre- 
ventive treatment of, 434-435 ; trans- 
mission of, 433 

Race improvement, necessity of, 362- 
363 ; suggestions for, 363-368 

Reactions, conscious, 219 ; glandular, 
221-^222 ; in learning, 219 ; levels of, 
216-217, 218, 219, 220; types of, 216- 
217. See Nervous reactions 

Recapitulation, doctrine of, 388-389 

Recessive character, defined, 324 ; list 
of, 333 

Red corpuscles, in lungs, 179 

Redi, Francesco, experiments on spon- 
taneous generation, 239-240 

Reduction division. See Maturation 

Reed, Major W., work on yellow fever, 

Reflex, conditioned, 217-219 ; develop- 
ment by conditioned response, 218 ; 
nature of, 217-219 ; simple, 215 

Refrigeration of foods, 399 

Regeneration, in amoeba, 56 ; in higher 
animals, 257 ; in lower animals, 256, 
257 ; similarity to vegetative propaga- 
tion, 255-256; in Stentor, 56; in 
Stylonychia, 56 ; in Uronychia, 56 

Rennin, 128, 129 

Reproduction, asexual. See Asexual re- 

Reproduction, by binary fission, 247- 
248 ; by budding, 248-250 ; by spore 
formation, 250-251 ; by vegetative 
propagation, 255-263 ; by two special 
cells, 264 ; necessity in cells, 246-247 ; 
of amoeba, 44, 248 ; of animals, 281- 
291 ; of bacteria, 247 ; of birds, 288 ; 
of frog, 282-287; of higher plants, 
273-279; of mammals, 288-291; 
of mold, 264, 265 ; of Paramecium, 
49-50; 248; 267-268; of Pleuroccus, 
247 ; of Spirogyra, 247-248, 265-267 

Reproduction, sexual. See Sexual Re- 

Reproductive glands, relation to normal 
development, 200-201 ; secretion of, 

Reproductive processes, in organisms, 
purpose of, 34 

Reptile, flying, 382 

Reptilia, animals of order, 526 

Respiration, 177-185 ; definition of, 182 ; 
external, 183 ; hygiene of, 185 ; in- 
ternal, 183 ; in plants, 36, 38-39 ; of 
amoeba, 44; of iish, 177-178; of 
insects, 177 ; of higher animals, 178 ; 
products of, 182-183, 184 ; rate of, 183 

Respiratory, movements, 181-182 ; pas- 
sages, irritation of, 179-180 

Respiratory tract, diseases of, adenoids, 
179 ; tonsillitis, 180 

Response, laboratory problems, of plants 
to gravity, 202-204 ; to sunlight, 203 ; 
to water, 204 



Reticular theory, of nature of protoplasm, 

Rhinoceros, prehistoric, 378 

Rhizoda, classified, 521 

Rhizoid, of mold, 251 

Rhizomes, plants with, 261 ; propaga- 
tion by, 261 

Rhythmic segmentation, of small intes- 
tine, 130 

Rickets, cause, 102-103 ; prevention and 
cure of, 100, 103 

Rodentia, classified, 527 

Rootstock, plants with, 261 ; propaga- 
tion by, 261 

Root hairs, of plants, 69 

Ross, Major R., investigation of malaria, 

Rotation of crops, need for, 409-411 

Round worms. See Nematheliminthes 

Roux, isolation of diphtheria toxin, 451 

Runners, use of, in propagating, 260-261 

■ Saliva, composition of, 121-122; diges- 
tive action of, 121-122 ; enzymes of, 
121 ; factors influencing secretion of, 
121 ; functions of, 120-121 ; secretions 
of, 121 

Salivary glands, position of, 120; func- 
tion of, 120-121 

Saponification, in the digestive process, 

Saprophytes, group of bacteria, 251, 394, 

Scarlet fever, probable cause of, 458 ; 
test to determine susceptibility to, 458 ; 
transmission of, 459 

Schleiden, knowledge of cells, 28 

Schultze, contribution to cell theory, 29 

Schwann, Theodore, work on cells, 28 

Science, age of, 1-3 ; aim of, 6 ; and 
health, 417-419 ; contributions by 
Greeks, 10-12; growth of, 10-11; of 
primitive man, 10 

Scientific method, modern, 13-15 * 

Scurvy, 97; cause of, 100, 102; treat- 
ment for, 100, 102 

Scyphozoa, 522 

Secretagogues, 128 

Secretin, 133 

Secretions, internal, 191-192 ; of green 
cell, 40 

Seed, appendages, 294 ; differ from eggs, 
281; dispersal of, 294-295; food re- 
serve of, 294-295 ; formation of, 278- 
279 ; protection of, 294 

Segmentation, rhythmic, of small intes- 
tine, 130 

Segregation, of genes during maturation, 
325, 328 ; Mendel ian law of,, 324-326 

Selection, artificial, importance in plants, 

Self-acting nervous system. See Au- 
tonomic nervous system 

Self-pity, as trait of personality, effect of, 

Serum of blood. See Blood 

Sexual characters, secondary, 281-282 

Sexual reproduction, in higher plants and 
animals, 264, 268, 273-291 ; in mold, 
264-265 ; meaning of, 264 ; in Parame- 
cium, 267-268 ; in Spirogyra, 265-267 

Shick test, application of, 457 ; of sus- 
ceptibility to diphtheria, 453 

Side-chain theory, of immunity, 506 

Sieve tubes, of plants function of, 68 

Simiidae, 527 

Simon, Theodore, tests by, 228 

Sirenia, animals "of Order, 527 

Skin, functions of, 173-174 ; hygiene of, 
174-175 ; laboratory study of the, 170- 
171 ; organ of elimination, 170, 173- 
174 ; sense organ, 173 ; structure of, 
172-173 ; thickness of, 172 

Slant, agar, 397 

Slips, method of vegetative propagation, 

Small intestine, absorption from, 136- 
137 ; adaptations of, 136-138 ; diges- 
tion in, 130-131,132-133, 135; diges- 
tive juices of, 132-133 ; folds in, 136 ; 
glands of, 131; movements of, 130; 
villi of, 136, 137 

Smallpox, cases and deaths in United 
States, 424 ; epidemics of, 420 ; history 
of, 420 ; history of inoculations against, 
420-421 ; nature and symptoms of, 
423, 425 ; preparation of vaccine for, 
426 ; prevention, 425-426 ; spread, 
425 ; value of vaccination, 426-427. 
See Vaccination 

Soil, bacteria of, 405-411 ; conservation 
of, 411 

Somatic cells, 269 

Somatic variations, not transmitted, 310 

Spallanzani, on spontaneous generation, 

Spawning, of fish, 283-284; of frogs, 

Species, production of new, 347-349 ; in 
taxonomy, 517 

Species and Varieties, by De Vries, 376-377 

Species, Origin of, by Darwin, 373 

Specialization, in higher plants, 69-72 

Sperm cell, characteristics of, 268 

Spermatogenesis, meaning of, 269 

Spermatophyta, 520 

Sperms, production of frog, 285 

Sphincters, 125 

Spillman, production of hardy wheat by, 

Spinal cord, description of, 207-208; 
diagram of cross section, 208 ; func- 



tion of, 208 ; level of reactions of, 218, 
219, 220; relation to reflexes, 208; 
structure of, 207-208 

Spireme, formation of, in cell division, 

Spirilla, form of bacteria, 392 

Spirochaete, causative organism of yel- 
low fever, 492 

Spirogyra, description of, 31 ; labora- 
tory problem on the cells of, 31-33; 
meaning of, 32 ; reproduction of, 247- 
248 ; 265-267 ; specialized structures 
of, 32 ; typical green cell, 31-37 

Spleen, activity of, 200 ; location of, 200 

Split-proteins, poisonous, formation of, 

Sponges, use of bacteria in preparation 
of, 404 

Spontaneous generation, controversy on, 
242-244 ; experimental evidence on, 
239-241 ; 242-243 ; theory of, 239 

Sporangia, laboratory problem, in vari- 
ous molds, 252 

Spore, of bacteria, denned, 395 

Spore-formation, cause of, 250 ; of yeast 
cells, 250 ; reproduction by, 250 

Sport. See Mutants 

Sporozoa, 521 

Stanford Revision of Binet-Simon scale, 

Starch, digestion of, 130 

Steapsin, 131 

Stentor, regeneration of, 56 

Stomach, function of, 129 ; glands of, 
125-126; of frog, 115; parts of, 152; 
shape of, 129 ; valves of, 125 

Stomata, of leaf, 67, 69 ; guard cells of, 
67 ; position of, 67 

Storage, of food in plants, 70-71 

Structure, of amoeba, 42 ; of Paramecium, 
46-47 ; of cell, 53-55 ; of protoplasm, 
55-57 ; of higher plants, 66-72 

Struggle for existence, 373 

Stimulation, of glands, chemical, 121, 
128; mechanical, 121; psychical, 121, 

Stimulus, meaning of, 40 ; of glands. 
See Stimulation 

Stylonychia, regeneration of, 56 

Sublingual gland, in mouth, 121 

Submaxillary glands, in mouth, 121 

Succus entericus, 131, 132 

Sunlight, in relation to rickets, 103 

Supporting tissues, in man, 77; in 
plants,, 71 ; laboratory problem on, 

Surgery, antiseptic, 4; aseptic, 45; 
early, 3, 11-13; grafting in. 259-260 
modern methods in, 13-15 
Survival of the fittest, 374 

Sweat glands, 171, 173 

Sweet peas, Mendel's experiments in 

heredity of, 322-326 ; 327-330 
Symbiosis, denned, 394 
Sympathetic nervous system. See.An- 

tonomic nervous system 
Synapse, properties of, 208, 209, 21